There is a coincidental factor, though. Obama claims to have written the book in Bali, over a six-month time frame.
Who else was in Bali at the time?
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.
They wouldn’t have had to be in Bali at all. Even if Obama was necessary for interviews/checking drafts, etc., it could have been done remotely. Bali has long-distance phone service and I believe DHL delivers.