The other thing is that if they caught this midstream, before he had finished his run, it's possible that somebody on the floor recognized him and brought the issue to the appropriate party.
I actually know somebody that happened to, though it was caught before he got the chance to even play. I'll keep things very generic to avoid naming names, but he had successfully applied to be on a show, and had made it into the studio, minutes away from playing as a contestant, when an industry professional recognized him to be an industry professional, and he was sent packing.