While that's mostly true, to use a db efficiently you need to have a bit of an idea of what it does inside.

I don't see that question as being any different really. They're both just ways of guiding a conversation around the area we work in to gauge what candidates know / are interested in.

Personally, I've poked around in Postgres a bit because I find it interesting. And having deeper knowledge means that when you're about about to add a new not null column with a default value to a massive table you can stop and reason through how you're about to shoot yourself in the face :-)