Apparently he'd been on back in '99, and then again last week, and it was fans of the show that recognized him. (Which is impressive in and of itself. Or borderline scary, you Trebek-heads.)
The fact that he got past producers is one thing, or the fact that the Rainman-like viewers remembered his face, but the real crime is this:
PLUS he scored a thousand bucks that first time! He couldn't set aside a hundred bucks for some new threads?!