He's written this kind of book before based on his time as a tabloid reporter and editor.
Indeed "The Insider" was the book that got him in all kinds of trouble since it sort of suggested that he knew all about so-called phone-hacking when he's claimed all along that he knows nothing about it.
His previous book has also been a little "free" with the factual accuracy. Certainly the suggestion seems to be that rather than keeping an actual diary, he re-imagined what his diary might have looked like. Hence dates and times are wrong etc.
I didn't read his tabloid book as I find the man odious. That said, it is supposed to be good fun. So who knows how his CNN book will end up.
Adam