I'm not sure if your numbers are accurate, but hypothetically speaking, IF that is the case, it could be similar to the situation in american sports, or Brazilian soccer, where class plays into it.
It isn't that black athletes are necessarily better, but there seems to be a larger number of kids from low income backgrounds that view a sporting career as their only viable option of getting out of poverty, and in a lot of countries, many blacks come from low income backgrounds.
There are successful rich kids and white kids in sports too, don't get me wrong, and some of them do go on to have pro careers, but when you're a poor kid out in the street with nothing else to do but kick a ball around and dream of a better life, I'm sure it helps you get there, skills wise.
Average joe white kid (or pierre) may be great at soccer too, but if he also has options for medical school, he might make that choice instead.
I'm only basing that on my personal observation that a lot of famous athletes from all races seem to come from poor and humble beginnings.
I have no stats. None of this is asserted as fact, just hypothetical pondering.