Those guys were not the Backstreet Boys, although one of them did look like Nick Carter. They were some guys hired by the folks running the ebay convention. Al didn't know anything about them until just before he went out there to sing. Al was really singing, but those guys were lip-syncing to a backing track.
Haha, yeah, I could pretty much tell they weren't. There's an African American guy in the group behind Al, and there is no one of that persuasion in the BSB. No one in that ebay group looks like A.J. Mclean, either. That's probably a good thing.