The film was historical fiction. It didn’t claim to be ‘true’.
Problem is too many uneducated people will take it to be true. A case in point is LITTLE BIG MAN from 1971. You would be shocked at the number of people who got their history lessons from a movie script.
‘Little Big Man’ was an adaptation of a novel.
Did you know that ‘Little Big Man’ and ‘Bonnie and Clyde’ were both directed by Arthur Penn when you brought up the former?