Answer

The question is what counts as heretics. A Torah scroll written by a heretic is burned. But academic commentators are not necessarily classified as heretics. Some halakhic decisors wrote that if a book contains verses but that is not the main part of the book, it does not require genizah, but that is an unusual opinion. All the more so here, where that actually is its main content, since the whole book revolves around interpretation of the Bible.