It's not racist at all, him having more fast-twitch fibers and him being black aren't related, as far as I know. I don't think race is a factor at all.
If you think that people can be as good as they will themselves to be, will yourself to grow a half-foot taller, and see how far it gets you.
That might seem silly, but it's not. Not only have your genes determined how many fast-twitch fibers you have, they have determined just how much you can improve them with exercise. In other words, some folks have lots, some don't. For some, targetted exercise will help a lot, for others, it won't do nearly as much.
It's somewhat similar to how "muscly" you can get without resorting to chemical means: You already have as many muscle cells as you're going to have. When you get bigger, you don't grow more cells, the cells just get bigger - and there is a limit to how large they can get. Folks who are born with more muscle cells to begin with can grow larger - and have an easier time doing it.
Genetics doesn't say "You were born with these genes, so you will be exactly this." Rather, they say "These genes mean that you are pointed in this direction, and have this much latitude to change it." Both the direction and the latitude to change vary from person to person.
When I was younger, I put on about 30 pounds of muscle over a couple of years, and I worked my freaking BUTT off to do it. One of my friends (who wasn't on the juice) did the same thing in a year, not working half as hard as me. My easiest muscles to grow were in my back, those were his hardest. I can't grow my calves for squat, his got bigger if he walked up stairs. He was one fast dude... but not a lot of muscular endurance. I can do very heavy things for long periods of time, but I'm not fast at all. Everyone is different.