The rate among blacks for several of these is quite a bit higher than for whites - other ones, like Marfan's syndrome, are not.
It's certainly not exclusive to black athletes.
It does appear to be genetic given his brother's problems (needing a heart transplant at age 25). How sad for his family, no doubt having spent their time worried about their sick older son only to have their apparently healthy son die suddenly. And with the complications that can arise from a heart transplant, the older son may not be out of the woods yet.