Had he been a Brazilian, Haitian, Saudi, Scotsman, etc. and traced his slave ancestry from some other country, would his movie be produced? Probably.
In Brazil, people would probably watch a movie about a Brazilian slave and his descendants.
In Haiti, people would probably watch a movie about Haitian slave and his descendants.
In Saudi Arabia, people would probably watch a movie about a Saudi slave and his descendants.
In Scotland, people would probably watch a movie about a Scottish slave and his descendants (especially if the slave-owner happened to be English).
Some things are make-the-USA-look-as-though-it-is-the-cruelest-nation-on-Earth sort of things. This isn't one of them.