I said 99% of athletically gifted kids (and for Ethiopia - maybe slightly less for Kenya which does do a few other international sports at a decent level by African standards).
The point about the sprinter is not really relevant - being a sprinter - but if anything it proves my point. He chose sprinting over rugby because there is no route to becoming a professional rugby player in Kenya. In the UK, Australia, New Zealand etc, I'd guess that 95% at least of young athletes equally talented in rugby and track would choose rugby.
The elite British sprinter Adam Gemeli was a moderately talented footballer. He was offered a contract by a non-league side, and apparently it tore his hair out trying to decide whether to choose that or represent his country at his home London Olympics.
BTW, your parrotted line that football is far more popular than running in Kenya is probably another proof that you have never set foot in Kenya. According to many sites, the most followed football club in Kenya is Gor Mahia, which has an average attendance of just 5,000 per game. The players for the club earn an average of just $600 per month. As far as I know, there are only 3 Kenyans playing professionally in European leagues.
Even if it was true that most Kenyans prefer to play football, there is no way that professional football is creaming off top running talent in any comparable way to it does in GB and Europe.