The fighter told him about his gruelling training sessions, how he lost 30 pounds in two months for a fight, and how little he earned.
Essentially, he was losing money fighting.
So Feng, a San Francisco-based actor-filmmaker, went to one of his fights to support him. The fighter lost.
The next day Feng ran into his neighbour again.
"They want to pay me a lot less now because I lost," Feng recalled the fighter telling him.
"I was like 'Wow, that's ridiculous.' And he was telling me 'I don't know if I want to keep doing this. It's too tough. I put so much into it and now not only am I losing money training and fighting, now they want to pay me less. It's a slap in the face.'"
Out of that conversation — and the ones that followed — came the idea for "Fight Life," Feng's documentary look at the hard, unforgiving world of MMA.
"It's really the best documentary I've seen on fighting by far," said UFC welterweight Jake Shields, one of the fighters featured in the movie. "There hasn't really been anything, at least not that I've seen yet, that's been really showing the fighter and this shows a lot."
As Feng began to explore gyms and meet more fighters, he learned more about the hardscrabble world of mixed martial arts.
"Everybody had these crazy stories, where they didn't make any money," he said. "And I was like 'Are you serious? You guys are doing all this for no money? Like that's unheard of. I don't know why anybody would do that.'
"And that's when I saw how much these guys love the sport of mixed martial arts and that really drew me. Their lives really paralleled my life as an independent filmmaker. So because of that connection, I pretty much just dove right into that sport."
The 28-year-old Feng had no investors, pouring his own savings into the project.
Feng did the premiere — two soldout screenings Jan. 20 at San Francisco's Roxie Theater during a rainstorm — on his own dime. He rented the theatre himself, paid for the posters and flyers and, in making the 80-minute movie, relied heavily on the goodwill of volunteers.
"There was no money behind it," he said.
"It's a hustle, it's definitely a hustle to get your film out there," he added. "And it's really difficult to be an independent filmmaker in this day and age when the economy's not so great."
To help pay the bills, he spends weekends as head of security at a local nightclub. He's worked in restaurants, delivered magazines and food for catering companies, coached tennis and basketball, and edited and shot videos for Yelp, a social networking review site.
"Just all kinds of stuff to get me by, because I'm waiting for my big break and I'm working my ass off to make sure that I can stay afloat and I'm not going to be in debt."
He's had offers for the film, but say he has yet to get the right one.
Feng spent three years on the project. He started shooting in 2009 and when done, found himself making one revision after another as the sport kept changing and evolving.
The film focuses primarily on Shields and Lyle (Fancy Pants) Beerbohm, using their stories to illustrate the challenges of the sport.
When the film was shot, Shields was on the verge of winning a title in Strikeforce to add to championships earned in EliteXC, Shooto and Rumble on the Rock.
In the aftermath of Feng's film, the San Francisco fighter subsequently joined the UFC, losing to Georges St-Pierre in a title shot last April before 50,000-plus in Toronto. More recently he defeated Yoshihiro Akiyama in Japan.
"I saw the whole rise of Jake Shields, how he went from a good fighter that was fighting on TV here and there to now — a star in the UFC," said Feng.
Further down the fight food chain, Beerbohm was a former meth addict who decided to become a fighter after seeing MMA on TV in prison. He phoned his father behind bars to break the news.
"I literally thought he was on drugs, he had got them somehow in the prison," his father Gene Beerbohm relates in the movie.
But Lyle stayed true to his word. On his way back from Walla Walla state penitentiary, he saw an MMA gym in Spokane and ordered his parents to stop the car.
"That was my first night in practice and I fell in love," he said.
His first fight — in 2007 — was eight days out of prison. He won his first 16 bouts but has since lost his last two in Strikeforce.
When he moved back home from prison, his mother Sherry had to move her fabric collection out of his room. He was helping her and asked her to make him a pair of shorts out of one of the more colourful samples.
She eventually did — and the nickname "Fancy Pants" was coined by the wife of a fighter at a show a week later.
"I took off my warmups and the crowd went wild," Beerbohm recalled of stepping into the ring. "The girls were whistling, the guys were laughing. It was a hit right from the get-go."
Beerbohm wears his love for his family on his sleeve. He clearly knows the pain he put them through before finding a rock in MMA.
"I can't say sorry enough to them," he says in the film. "But for me to actually make them smile, that makes me feel so good. To actually have them be proud of me, that's a great experience."
It's a genuine feel-good moment and speaks volumes for what the sport can do to change a life.
Beerbohm is also profiled in a separate project called "No Submission: The Lyle 'Fancy Pants' Beerbohm Story."
Feng says he originally wanted to focus on three fighters but cut it down to two after filming because one of them lost three fights in a row.
"And he got knocked out badly in some of those fights," said Feng. "And this was after we had done the filming and everything. He asked me if I could not show any of that footage ... He said "Hey, I don't want my kids to see this kind of stuff and see me getting knocked out a million times — and it's in a movie, forever embedded in cinema.'"
Feng agreed and went with Shields and Beerbohm. He declined to identify the third fighter.
"Fight Life" also excels at showing the tight ties between teammates.
Beerbohm and his fellow fighters bang and bloody themselves in their Spokane gym — then happily talk about the bond they share.
It's the same for Shields and training partners Nick and Nate Diaz and Gilbert Melendez, all elite fighters in their own right. It truly is like a band of brothers.
Iron sharpens iron in the world of MMA training.
"A lot of people think MMA's an individual sport, because there's only one guy fighting in the Octagon or the ring," Feng explained. "But if you actually see what's going on behind the scenes, and what it takes for that guy to get to the cage, then you understand that this is actually a team sport."
Anyone who thinks they have the skills to do it themselves is in for a rude awakening. That's something else Feng wanted to portray so the next generation of fighters knows what awaits them.
"Why don't you watch 'Fight Life' and you get to see what it's like to be a fighter? . . . Because I think that's the thing to say now — everyone wants to say they're a fighter."
As he started delving into his subject matter, Feng, started asking around and the name that kept on popping up in the Bay Area was Shields.
So Feng looked him up on the Internet and called his manager, who was Shields' father. He laid out his vision for the documentary and was invited to the gym.
Feng watched Shields train and then had lunch with the fighter. "And then the rest is history."
Those in the know pointed him in the direction of Beerbohm and his prison-to-gym story.
Feng found fighters and others in the sport also more than willing to open up, to show that MMA is more than the bright lights of pay-per-preview, the spotlight of a TV main event of or prime-time show portraying the champion "driving a nice truck."
"You think these guys are millionaires," said Feng. "For me it was like how about let's capture the guys before they were millionaires, before they were big-time guys."
While Feng revised his film, other MMA projects started trickling out. The list includes "Fightville," "Like Water" and "The Striking Truth" by Canadian director Steven J. Wong.
Feng isn't bothered, saying each is different.
"A lot of these documentaries are just solely focused on one fighter and for me, I really wanted to make a documentary on the whole sport of MMA," he said.
He also found the sport was changing. The UFC bought out Strikeforce and introduced health insurance. Shields moved further up the fight ladder.
"We were done a while ago but we had a lot of issues to deal with," he said. "For me, it was important that I get it right."
Strikeforce co-operated in the filmmaking — "a huge support" — with Feng crediting Shields and former Strikeforce staffer Mike Afromowitz for helping pave the way.
He gave Shields a co-producer credit, essentially to thank him for his time and resources. The fighter opened a lot of doors for the filmmaker, putting him in touch with the likes of former UFC champion Chuck (The Iceman) Liddell.
"He (Shields) said that he wanted to really show people the real life of a fighter," said Feng.
Feng studied acting at University California, San Diego, and spent two years acting in Asia before turning to filmmaking.
"Fight Life" is his first full-length film after several shorts.
In addition to San Francisco, Feng's film has been shown in Portland and was slated to be screened Tuesday in New York as part of a Legalize MMA rally.
He also has plans for a mini-tour of California and a free screening at his alma mater, UCSD.
Feng hopes to get the film on TV and DVD after that.
"My goal with this film was to get it out to as many people as possible," he said. "It's really not about making the money or anything like that."
On the Internet, http://www.fightlife.tv/