I'm pretty confident both of you are people I'd be happy to work with in the future and so I want to use this as an opportunity to point out that your reaction to what Kasey said his reaction would have been to your interview question practically guarantees that you would fail to acquire Kasey for your team. I know Kasey a little bit better than I know you (he's a Chicago person) so I'll just sum this up as "that's not a point in the win column for this interviewing strategy".

I know you're not asking people recite "ps" flags from memory. The problem is, you're looking for a subjective "X-factor" in how someone answers a trivia question.

I used to really like this approach too. I'd think of things that you'd only know if you'd actually done the kind of work I'd done. I had some favorite interview questions: "what are some of the functions you carry around with you from project to project in your 'libyou.a' library", and "where would you start looking if you had to debug a program that segfaulted in malloc"? I think the logic I was using is the same as the logic you're using here.

Ultimately, I think it's a bad approach. Equivalently strong candidates look at their work through different lenses, and find different things memorable. Far more important to me, though, is that some people really suck at interviewing --- and, what motivates me more, having succumbed to this repeatedly as a hiring manager and also being myself I think an example of the phenomenon --- some people just interview way better than they should.