Big difference with Mr. Otis. He is quoted as saying “IF society dictated that one had to be black or white, I WOULD be Black.” Words matter. Both parts of the sentence are in the subjunctive, which here is making a “contrary to fact” thought.
A well known expression of the same sort is: “If my grandmother had wheels, she’d be a truck.” But she does not have wheels, so she’s not a truck.
People did assume that Johnny Otis was black. No one ever thought Al Jolson was.
And when it comes to records, black audiences thought a number of white performers were black until they took the stage (or appeared on tv).