So you think everyone that repeats that stereotype has the knowledge that it came from decades ago and that's what they're implying?
Because, every single time I've seen it mentioned is when a black friend doesn't want to swim when everyone else is going in the water, in this decade. I've seen guys just not knowing how to swim and girls not wanting to get their hair wet and that's why it gets repeated.
Not one person ever said "I can't swim because I come from a long line of ancestors who weren't allowed to swim and it somehow became a part of my genetic code".
Just because something has a history, doesn't give it more weight in a time where it's all but forgotten and doesn't carry the same meaning.