He's used to debating 20-something people on subjects that he himself has studied. He himself does not answer questions, he pulls out stats and whatnot and is on the offensive, sidestepping questions and then makes edited clips about the best "owning the libs" moments. One of the more important aspects in his style of debating is to make sure that nothing is about him or his beliefs. Always put the focus on the other person so that you can point out their flaws but never allow yourself to be the focus and never admit to holding a position because that position could be flawed.
Then he ended up in an interview...
Where he is supposed to answer questions AND explain his positions and arguments in the book. That's not what he is used to, that's where he is the weakest. So of course he panicked, he might have been forced to admit something of his own beliefs. Granted that answering the questions normally would been less embarrassing that practically running away crying after accusing the right-wing interviewer of being a leftist, but in a panic he fell back to his normal playstyle.