War of the Worlds doesn’t meet the criteria.
It quite literally caused a national panic, because it was delivered in a believable manner to a gullible audience.
American hustle is clearly a movie.
It's a biopic that presents itself as a historical account of real life events.
Historia Regium Brittanie seems like it might fit the criteria, but I suspect
You're going to have to put more on the table than "it doesn't count because I would have known better if I'd read it in 1163".
What I was trying to say is thst its impossible to have an author create a piece of fiction, written as factual, purely for entertainment purposes, while maintaining that it is factual.
It is incredibly easy.