yeah, same here, I was like "wow what an interesting side to their business, a whole operating system intended to serve public and academic libraries!"
I think parent poster was referring to an actual library, i.e. where you would borrow books.
That's also what I thought this was, and came to the comments expecting to see something neat about why libraries might need bespoke operating systems.
Ah right! Yeah, I did think that too..., like locked down so random patrons couldn't do this or that. I was thinking that was quite a pivot for MS though too...