Sadly, the word "ban" has been used all too inapropriatley lately. And this website doesn't seem to help as nowhere did I see exactly what they meant by banned, who banned them, or exactly what the ban entails.
Banning, in this case, means removal from libraries. Sometimes it is by state order, sometimes it is via independent action taken by the school district (although that is usually also in an attempt to adhere with state board of education guidelines). The linked data source cited for this article provides ban classifications for each and every book they list as banned.
>Namely, they are not and have not been about the physical removal of a book from a shelf.