If he claims he was in Bali, then I doubt anyone else was there helping him write a book. The ghost writer was back in Chicago, and he was taking time off, but not being around anyone so that no one could see he wasn’t at a word processor all day. I don’t know the contents of the book, but if I was writing about my life in Chicago, I would be in Chicago writing it, in order to verify facts, and locations.
However, if I were the ghost writer, I would require some major face time with the person whose "autobiography" I was writing.
That's assuming the whole thing is not a fabrication, of course.
If there was a ghost writer, he would have been in Bali for at least some of the six months.