They most likely formed in northern Ethiopia/Eritrea before heading your way.That's a semantics game and nit-picking, but you get the point, they came from the area somewhere between Egypt and Eritrea. They definitely didn't come from Ethiopia that's for sure.
No evidence of Khoisan admixture in Somalia. Somalis are the least hunter-gatherer like of all Horn African groups, even less than the Tigre-Tigray.