yes, actually, that's true. take for example runners from Kenya, they have thinner bones/sceletons than white people which again makes their bones lighter and therefore they are better able to maximize their ability to run long and fast. and of course like you mention it has a great deal to do with cultural things like how you live, work out etc.
but Demonic69, what you were told by your moto instructor, I don't think it's got anything to do with balance that black people mostly don't ski. that just sounds a little bit far off. but idk