Something like that would have taken extra time and effort, and the problem took care of itself. He had more important things to focus on.
And I think it would have been more difficult to catch than you think. We don't do pair programming, and it's kind of reasonable to ask for time to figure something out. I think the best he could have determined was the guy wasn't good, not any of the suspicions about the scam of cheating on the interview and getting outside help.