It implied the Librarian knows her area of research and either happened across a book he knew she would be interested in or was actively searching on her behalf.
Worth bearing mind as well that Ruby has a tendency to embellish these kind of things, choose misleading language or outright lie to make herself seem special.
She did it a lot at Exeter and tried to make it seem like she was some kind of VIP on her course or every tutor's favourite student, when she was either making stuff up or misrepresenting everyday meetings and blanket emails that were sent to all students and acted like they were just for her.
She's always been a relentless suck-up with tutors and faculty (sending them unsolicited letters, cards and gifts constantly), so it's entirely possible she has made an effort to speak to the librarian there whenever she's there, they remembered one of the areas of study she feigned an interest in or asked about and were nice enough to ask if she'd like to view a text they came across that they thought might interest her.
But it's also likely that she just put in a standard request to view a manuscript mentioned on her course that was in the library's archives and then she got a boilerplate email from the library to confirm she could view them at a certain time, then she embellished from there.