Cullen Jones won gold as a member of the US 4x100 Free relay. http://en.wikipedia.org/wiki/Cullen_Jones

That's not related. Why are there no World Class Kungfu Masters from Zimbabwe?

It most certainly is related. If the author of the article is questioning why one race dominates in a certain sport, then asking the follow up question of why that same race is noticeably absent from a different sport is related. We're talking about black people and why they do well at some sports; you could also talk about black people and why they seem not to do as well in others.

And a world class zimbabwean kung fu master could exist.

It has nothing to do with race. East Africans are of the same 'race' as West Africans. Your concept of 'race' has nothing to do with reality - you can't just take the color of peoples skin and group them all together. It's very superficial, and is totally unrelated to any biological reality.