Hidden or unexpected, it was still an unknown. Just because it wasn't a secret didn't mean everyone knew about it which made it... Maybe not so much hidden, but certainly surprising. "Those are my favorite kind." And they were. Honestly, the older the books, the better.
She wasn't wrong, and Mircea had definitely referred to himself as such not that long ago, but still... "I guess. Personally, I've always had trouble wrapping my head around that."