I remember hearing during the Olympics them actually talk about how much of a freak Bolt is to be so tall and so fast. Most runners are on the shorter side. For those that watch the NFL you'll know that being tall and fast is what makes people DK Metcalf such a freak of nature when sprinters are actually usually smaller, like Tyreek Hill. It's less about stride length and more about power put into the ground which is easier for shorter legs.

If you watch Bolt run you'll notice he doesn't actually hit his peak until way after the other runners during the 100m. He has said before iirc that he's actually a more natural 200m runner rather than a 100m runner. On the 100 he barely gets to his top speed before the finish. That's what makes his 100m records truly so phenomenal, he's not really built for that race but was still so much faster than everyone else on the track.

It's not out of the realm of possibility that a runner from Nepal being Asian and therefore statistically likely to be shorter than someone born in Africa, could be a record breaking runner. Of course this is all about sprinting but over longer distances the longer lankier bodies prevail, better momentum.

tldr: short legs go zoom, long legs go long.

Interesting....not what I expected

As OP and not the poster you are asking, I'll answer this one:
Ethiopians and particularly Sudanese (then zooming in even more specifically - the Nuba tribe) are known for being among the tallest people in the continent today.

It was right around this area where the Kush people of the Nile Valley Civilization flourished in antiquity. The Kush are described by accounts of the era as being taller than any other Mediterranean groups.
Relative genetic isolation since then results in that they were tall then, and they are tall now. Some of this genetic heritage must have also spread down to Kenya in the interim.