Questions of school library censorship have always been about age-appropriateness, or blasphemy, or antiquated common but now forbidden ideas. If not buying and not accepting donations of that material isn't a ban, then what could possibly be? If it does count as a ban, every school library now has to carry the complete works of Lyndon LaRouche?
edit: a real ban on bans in my eyes would be a state restriction on local governments passing book bans that apply to public schools and libraries. It wouldn't be aimed at the libraries themselves.