This is not necessarily true. Eastern Oromos in areas like Bale, Arsi and Hararghe who are by far the closest people to us genetically are not that high in Mota ancestry, last I checked. And those guys were largely predated by what looked to have been Sidamics and Somalis in those areas based on inspecting the Futux al-Xabasha. I imagine them to have been a conduit for this. And like I said, it is very, very strange how Somali MENA scores are EXTREMELY homogeneous once you ignore the few Boran admixed Kenyans:
That's a clearly very stabilized population. And I've seen this homogeneity remain across Somaliweyn. Galbeed to Koonfur, Jabuuti to Bari. Does it make any sense to you that one person is 3% Yemeni and another is 10% yet they all coincidentally cluster so tightly on PCAs and are pretty much equally MENA? There's something funky amok with the Yemeni scores probably to do with drift which is why sometimes folks who show 0% can suddenly show 4% or more if you run the right models.
All Yemenis carry some Horner admixture. Possibly anyway.