How likely, as pp have said, is the "librarian" to be a qualified librarian as opposed to someone working in the school library? Library science is about dissemination of information, one does not necessarily need an abiding passion for literature to take this qualification and be a successful librarian.
What does trouble me, however, is that a school librarian doesn't read at all.
Schools need to promote reading and engaging with literacy as part of lifelong learning. I'd therefore expect a school librarian to model reading and some sort of interest in literature. Is this not also a disadvantage when it comes to library stock in this particular context- particularly as I imagine school libraries have great demands on their funds and keeping teens of all abilities engaged is hard. Reading some of the books and having a working knowledge of them is surely knowing your demographic.
Similarly whilst I wouldn't expect a librarian to have read Wolf Hall, it became so mainstream, I am surprised they haven't heard of it in general. Particularly as they may have a few- not necessarily many- students who have read it, particularly 16 and up. Not all teens exist on a diet of YA fiction. I didn't at that age. I read some, but mixed in amongst plenty of other novels. Especially as magic/ fantasy was a big thing when I was a teen and I disliked most of it. If it had been there to read at the time, I would more likely have read Wolf Hall.
There are also some really inaccessible Booker winners that unsurprisingly didn't land with the public at all. Some are more readable but still have just moments of prominence before fading into obscurity. This one hasn't gone away. I first read Wolf Hall as a student studying the Booker Prize. A few of the books were "famous" and had transcended to a degree, but some of them were unsurprisingly unpopular/ unknown amongst the wider public.