I took a a look at the book. It claims Landy came back pretty fast after he was let go in late 1976, and that by '79 or so, Brian was still with Landy but evading his handlers to score drugs. There's also a picture dated 1974 with the Netherlands as a locale, with group members including Bruce, two years after he left. I've got my concerns.
Don't know the person, but if that's what he's saying, he's certainly clueless about the late 70's/early 80's. My guess is, he didn't interview anyone who was around then - certainly no one who knew anything.
Who ISN'T writing a book?