The only twist in this case may be that it's the conman making everything up rather than the movie producer / writer / director. "Based on a true story" almost always means, "totally made up, but doesn't contain any scifi or magic, unless it's about an exorcism."
“Based on a true story”: loosely based on a book
“Based on true events”: loosely based on some news articles
“Inspired by true events”: The writer heard your story and thought of a more interesting one
https://slate.com/news-and-politics/2004/03/is-hidalgo-reall...
Seriously though, I think that movie was what really broke the "based on a true story" thing for me. There's no real criteria for claiming something is based on a true story, you only need a tenuous grasp to reality.
Basically, you can make the claim that Avengers Endgame is just as much based on a true story as Hidalgo if you wanted to.