As much as this isn't an atttempt to "ban" the book it also isn't an attempt to "censor" the book. It's simply a publisher saying 'We don't want to publish this book in this form". And they could say that for any reason, including a political one.

Now, he may have signed a contract with this publisher that has the literary equivalent to a non-compete in it ( "You can only publish through us" ), but that's on him.