SjmarfBirthplaces of the 100 fastest 10,000m runners of all time
PowerCrazyThe topography explains it all. geology.com/articles/east-africa-rift.shtml
tl;dr The people of that area in East Africa naturally live close to sea level, however there are easily accessible elevations changes that distance runners have trained on for probably centuries. It turns out that training at high altitudes and recovering at low altitudes provides a tangible and demonstrable advantage compared to just single elevation training.
Yeah like the other commenter said this isn’t it, nobody is commuting up and down 10,000’ on a regular basis, especially in antiquity. Just because different elevations “look close” on a map means nothing.
Far more likely is this is a concentrated population of folks with highly desirable traits for distance running.