Its probably more to do with their 70s haircuts....
No, this is a social not intellectual experiment, he isnt denying his own sanity, he knows the answer but is more concerned about being embarrassed by choosing differently to everybody else.
Think about it, if he chooses the same as everyone, if by chance his correct choice was wrong and the group answer is correct, then everyones a winner.
If its announced everybody is wrong then, he is wrong with everybody......so still a winner socially.