The web site says: "The ALA defines a “challenge” as an attempt to remove or restrict access to a library resource, while a “ban” refers to the removal of materials from a library"
Page 10 of the report has a chart that breaks down what type of people are responsible for an 'attempt to remove' books from a library. Librarians themselves are not listed as one of the groups:
It seems they only count it as 'censorship' or a 'challenge' if it's someone other than a librarian taking the action.
If I've understood correctly, if librarians (alone or in groups) decide that certain books should not be procured, the ALA would count this as a censorship or ban.
> ALA defines a “ban” as the removal of materials from a library based on the objections of a person or group. A “challenge” is an attempt to have a library resource removed, or access to it restricted, based on the objections of a person or group.
Under that definition, it doesn't seem to me like it would be possible for a "ban" to happen without also being a "challenge".
That and, have you met librarians? They aren't conspiring to censor Sarah Maas, I can tell you that.