Right, you need to know certain things. But the point of the question is not that you know what a B-tree is a have memorized a fact about the btree. The point is the followup question, which requires you to understand the consequences of using different kinds of trees. That's not the sort of thing you memorize, it's the sort of thing you internalize. If you can't answer the second question, you probably wouldn't know enough about trees to be able to casually think about certain problems you might come across in "systems programming".

My school didn't teach B-trees, though they did teach 2-4 trees. I've never really been in a situation where I've needed to use a B-tree; and, I was an accomplished competition programmer in college.

That said, I looked up on the internet what they were and it was pretty easy to follow.

It would be very cool if there was a programming contest problem that required efficient disk access.

There are some problems that require efficient reading, which is from the disk; and some that require efficient writing --- though that's more of just "buffer your outputs and don't use complex print methods, like System.out.printf"