> I have not found the type of person who asks trick questions to be the type of person who finds it interesting to have the trick questions they've posed to be prodded.

I find it depends entirely on whether the person is asking a trick question to try prove themselves smart (and are sensitive about it), or as in this case, are confident in their own intelligence, and want to assess yours.

Not confident but overconfident in this case. Clearly nobody has ever told him it's a crappy question (unless you're interviewing for a math PhD or something), and wrong on top of that, and he didn't have enough self-awareness to double check. Or maybe somebody did tell him, but he didn't care to listen.