USADA CEO Travis Tygart, in an interview that aired Wednesday night during the show's premiere on Showtime, didn't discuss the meeting on camera and provided no details, including when it was held and where. The only mention, with no elaboration, came at the end of the segment.
Tygart didn't respond to messages left by The Associated Press seeking comment.
The New York Times reported last week that Armstrong and Tygart had been meeting about a possible confession. Armstrong's attorney, Tim Herman, denied the meetings had taken place.
During the show, Tygart detailed his mission to investigate Armstrong, calling the cyclist's refusal to help in the probe "one of the lowest days of this investigation, quite honestly."
"We were disappointed he didn't come in and be part of the solution," Tygart said.
Last October, USADA released a 200-page report detailing the doping program Armstrong ran. At the time, Tygart called it "the most sophisticated, professionalized and successful doping program that sport has ever seen."
If Armstrong were to confess, there could be legal consequences, involving past and present civil cases and possibly perjury.
In addition to having his seven Tour de France titles stripped, Armstrong was banned for life from competing, which makes him ineligible for triathlons and other events sanctioned by USADA or the World Anti-Doping Agency.
In the interview, Tygart said a representative of Armstrong's approached USADA in 2004 with an offer of a donation of more than $150,000.
Asked if it felt like he was being bought off, Tygart responded: "It was a clear conflict of interest for USADA and we had no hesitation in rejecting that offer."
Tygart also said he had been subject to numerous death threats from anonymous emails and letters.
"The worst was probably puttin' a bullet in my head," Tygart said when asked to recall specific details of the letter.
He said the threatening letters were turned over to the FBI.
Tygart also discussed the pressure he felt while pursuing the investigation, even after federal officials decided to shut down their probe. Last year, two members of Congress called for stronger oversight of USADA, which receives more than half its $15 million annual budget from the government.
"We're always concerned about the grant we get from the federal government," Tygart said. "If we're unwillin' to take this case and help this sport move forward, that we're here for naught. We should shut down. And if they wanna shut us down for doing our job on behalf of clean athletes, and the integrity of competition, then shut us down."