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.