Does it have a unique graphics or color? Can you write in it? Is it the type of book you can purchase from an NPC vendor? Sometimes players write their own stories, check to see if theres an authors name on the first page, or the last page of the story, also flip through it and look for grammatical errors. Alot of times thats a dead give away it was player written.
It could also just be one of those collectible story books.