Did Stephen King "invent" The Shining? Did Tom Clancy "invent" The Hunt for Red October?
He wrote it. From scratch. Using ideas gleaned from book.
Quit flogging this stupidly dead horse.
If he used a book, it wasn't from scratch. At least in my opinion, "from scratch" means with basically nothing pre-existing. According to his instructor Tannenbaum he used the existing Minix file structure, so it wasn't "from scratch", per my understanding of what that means.