They are just defining terms. I see a lot of confusion about this, and there's already a comment below equating curating with banning.

The mention of soft censorship (trying to remove a book from a library or curriculum) is to differentiate it from hard censorship (the government banning the publication and sale of a book). Again, there are always a few people on these types of articles trying to say that only hard censorship counts. Soft censorship is still censorship, and it's pretty much always the type that we're talking about in a U.S. context.