I think that the lines between fiction and non-fiction are always blurred in memoirs and autobiogrpahies - how could it be otherwise? It's just that as this one is criticising the RF, rather than the parents of a footballer or actor (who have even less chance of being able to defend themselves) people are getting upset.
Disclaimer - I would hate it if my children wrote exposes about me (not that they would run to more than a few pages
), as I do see it as a betrayal of trust, and also, ironically, of the need for a safe space to be yourself that a family home should provide - having your most private moments shouted to the world is very bad for the mental health that Harry is so keen to protect. I am not condoning the writing of the book, but pointing out that it is no different really from any other book about someone's childhood or family relationships, and memoirs do sell very well.