Why is it considered a "ban" when a library chooses not to shelve a book? This is a poorly written article aside from the paging format. I only read three pages

Why is it considered a "ban" when a library chooses not to shelve a book? This is a poorly written article aside from the paging format. I only read three pages of it but by the third I still had not seen any explanation of an actual banning. One it says was banned with no explanation, the other two it says were banned by libraries. I checked out Wikipedia and all three (Oz, Harriet and Merriam-Webster) were "banned" by school libraries. No student or family was prevented from owning or reading these books. The schools simply chose not to put them on their shelves, or removed them from their shelves, and might have publicly criticized them.