Oh, if it's just a joke that went over my head then that totally makes sense! Though in fairness there are apparently-serious interview questions that are even easier (e.g. FizzBuzz, though I don't think anyone asks that anymore either) and I've been asked interview questions that aren't much harder.

I mostly agree with your impression, though even after adjusting for intelligence I bet there's a positive correlation between knowing how B-trees work and, say, having a good intuition for how to index a database.