I'm not going to waste time discussing the kind of claims that the OP suggests.
But there's one interesting question here: why don't African athletes dominate cycling as they do the other biggest endurance sport -runninng?
There are many possible explanations aside from the PEDs extremely boring topic (although in principle, it can be a factor). Couple of possible explanations.
First of all, cycling and biking simply do not require the same skills. There's some overlapping here, of course, VO2, lactic tolerance, etc. So correlation between excelling at running and excelling at biking must be a thing. You have Michael Woods as an example, the Canadian 1500m guy who ran 3:39 when he was 20 and had to quit the sport because of injuries. He is now a TOP classic rider, although it took him some time. I am thinking about another Spanish duathlon athlete who ran 2.10' out of 80-90 km a week, plus biking. So biking probably helps.
BUT: they are different sports. So the correlation between excelling at running and excelling at biking is not perfect. You can be born to run, and just be good at cycling - and the opposite as well. I think that the main factor here is probably running economy. As far as I know, this looks like the biggest advantage for African runners. This advantage translates to +- 0 advantage in cycling. So, if their (likely) biggest advantage disappears in cycling, there's no point in expecting them to dominate cycling as well.
Moreover, as it has been pointed, cycling is not a thing yet in Africa, mainly due to "social" (cultural, economical, roads, etc) reasons Eritrea is a good example of that. They DO have the biking culture -I think because of the Italian influence- and they DO produce good cyclists. Actually, more than you would expect from a very poor, <6million people country, given the fact that biking is logistically and economically way more demanding than running. So I guess that probably IF other African countries had the same biking culture (bc the sport becomes more available/popular), they would be producing good riders (as Eritrea suggests).
I hope this to happen in the medium term¡