The record-breaking Kenyan distance runners come from a particular area of Kenya, the home of the Kalenjin tribe. A few years ago, there was a Kenyan studying at an American university who wasn't interested in running. Some friends realised that he originated from that tribe and ought to be a good runner. They persuaded him to take part in running competitions, and he was soon winning medals galore!
There seems to be a feeling about that it is somehow racist to enter into this kind of discussion. My own opinion is that if it is true, what is the harm in talking about it?
I went to school with a Kenyan who was pressured into running despite not being keen on it. He was much more more interested in physics and programming.
He was encouraged and promised how great it was going to be for him and he trained for years but was never quite good enough and the people who pushed him into running all showed their disappointment.
He excelled academically throughout high school, but in our final two years he was generally seen as a failure. He would often get jibes about whether he was really Kenyan all sorts of jokes/teasing like that.
He's a pretty successful electromechanical engineer now who runs his own software development company, and he still talks about how much he hated life in high school and how hard it was for him.
It's pretty fucking stupid to make any assumptions or have any expectations of an individual, whether 'positive' or 'negative', based on the color of their skin.
There's nothing wrong with discussing any research that shows evidence of characteristics that are more or less likely within a genetically similar group.
Imagine being Lukaku and having an average sized dick. It may not be offensive to hear the chant while on the field, but it would be pretty shitty when he meets a girl he likes and has to wonder whether she's going to be disappointed.
Shitty personal experiences due to nothing other than people having an expectation or preconception that you had no control over. That's what racism does.