Other than the story about how we worked with China to arm rebels resisting Vietnam's occupation of Cambodia, nothing in this book is actually new--if the bits in this article were selected because they are the most shocking.
We aided China--including military technology to assist them in resisting a potential Soviet ground invasion--because "Nixon went to China." Of course we focused on our common foe, the USSR. If not, the only point to "going" to any foe is to give up.
So no doubt the author got multiple permissions to publish.
Not that the book is necessarily bad. I have no idea. And just because the stories are little-known doesn't mean it isn't useful to remind people so they don't get confused about our current policies of extending open hands to foes.
That confusion about realpolitik explains defenders of the President's policies toward Iran repeatedly insisting this is a "Nixon goes to China" moment in history. Egads, the stupid hurts.