Basically it's like someone else said. They read a book and know a lot of answers, but they can't do the most basic implementation of a solution.
No, it seems about on about the same level as being able to paraphrase the abstract of a paper about the system. I would not take it as showing that someone has read past the first page. A high-level overview just isn't enough for that. You have to ask your own probing questions too. Limiting the conversation to the particular problems they bring up is essentially taking them at their word when they claim to be skilled. I've seen lots of occasions where trying to drill down for a bit more detail on some part of what they talked about consistently came up empty (without going anywhere near sitting down at a computer to write a fizzbuzz equivalent).