It don’t think omitting certain books from a library is the same as banning a book. Libraries curate their collections. They search out certain books and certain types of books in an attempt to create a collection they think best suits their patrons’ needs. Curating as a rule involves omitting certain materials when they are determined not to suit the needs of the collection because of their quality, purpose or redundancy. But being omitted from a library collection is a far cry from being banned (even when the omission is questionable). People are still free to buy, read and share any book they want, regardless of if it is included in a library or omitted from school curriculum.
On a related note certain religious advocacy groups have habit of donating large quantities of church published books coughmormonscough in hopes of employing libraries to spread their religion. Libraries are of course not supposed to push specific political or religious agendas and they do evaluate donated books before adding them to their collection. I read an article recently (which I sadly can’t find) about a Christian group that was outraged that a library had rejected their donation of homophobic children’s books.
If you’re interested in how books are included or excluded from a library I recommend looking up their donations policy.