Most of this has to do with the game or competition that is heavily in the race's culture.
Blacks are good at professional basketball because that is often their sport of choice. With hispanics, it's not always cut and dry; however. If you're Puerto Rican, Dominican, or Cuban, baseball is the most important sport. If you're any other type of hispanic, soccer usually takes priority. USUALLY!
These aren't universal rules, of course. It's just that, the more a person is surrounded by a certain sport, the more likely it is that he willl be good at that sport.