"Guys, I'm sorry," he said on NBC's "Today" show. "That wasn't my intention."
The Portland-area thespian's proposal last week to girlfriend Amy Frankel features about 60 people dancing on a small street near his parents' house and has notched more than 6 million hits on YouTube.
Lamb is pitching it as the world's first lip-synched proposal, and there don't appear to be any challengers.
The video begins with his brother putting headphones over Frankel's ears as she sits facing out the back of an SUV, her legs dangling over the rear bumper.
"This song tends to exemplify you and Isaac's relationship to me," the brother tells her, and there begins Bruno Mars' sugar-pop, up-tempo ballad "Marry You."
The car starts moving and two of the couple's friends roll into the frame, then a few more. It was nothing that seemed too out of the ordinary, Frankel told NBC's "Today." Lamb and Frankel are actors and are used to elaborate stunts.
Frankel thought: "Oh, they're doing something with Isaac's family," she told the show. "There's seven of them. This is so sweet."
A second camera — the one that gives the video its emotional heft — is perched above Frankel's face, capturing her reaction. It shows her as she crosses her hands on her chest, shakes her head and giggles. By the best estimates capable of conveyance by digital photography, she swoons.
Before Lamb's proposal, there was Jill and Kevin's wedding entrance dance from 2009, which set the standard for matrimonial cool and — at 75 million online views — spawned countless imitators.
Compared with the shaky, hand-held "JK Wedding Entrance Dance," Lamb's proposal is positively high-tech. It also is elaborate but not expensive, choreographed but not constrained. In this city where the television show "Portlandia" suggested young people go to retire, most of the people in the video look like they fell off the bus from Central Casting headed for its set.
For all the pageantry, though, the proposal itself was pretty simple.
"You have already given me a lifetime of happiness," Lamb tells Frankel when the music stops. "Will you let me spend the rest of my life trying to give you the same? Will you marry me?"
She nods, and they kiss as a man in the background wearing a marching-band costume wipes away a tear.
Asked on "Today" about her favourite moment of the dance routine, Frankel said it was when she first saw Lamb appear on the street.
"When they all parted, and there was Isaac," she said. "That was the first time I think I took a breath."
Isaac Lamb's proposal, https://www.youtube.com/watch?v=5_v7QrIW0zY
Reach reporter Nigel Duara on Twitter at http://www.twitter.com/nigelduara