Is the book canon? AU?

From the way the book is structured, delivered, inconsistent to the game at some points, as well as what people are saying, it appears to be an AU of sorts.If so, what's the point of the book? If it indeed isn't canon and is based off an entirely different FNaF, then why associate it with the game's plot?I mean, I don't mind it and I'm even looking forward to actually reading it, but then why tell it if it doesn't help with the storyline of the actual series? Is it basically meant to shed more light on what Freddy Fazbear's Pizza really is? Just to explain the characters and setting? Or is this truly the actually story, but we just assumed to wrong things from the game?I could be wrong, mainly basing this off of what the reviews and readers are saying. Can anyone explain this better? It would be very much appreciated! Thanks!