It's super interesting stuff, I'm still learning. But as a Somali, i'll never acknowledge or accept that Somalis come from arabs, I've also read that the somali language is also older than arabic, i'll send sources over once i get 'em. Either way one thing i do know for sure is that the African continent has largest amount of human genetic diversity and the origin of humanity, and that my people (somalis) have been around for a very long time and predate the modern arabs. Just because of our faith and different features people assume we're arabs, or are products of them.
I wasn't saying that Somalis "came from" Arabs. But the genetics suggest that Arabs were part of the mix. According to that study:
Ethiopian Somali: 38% Eastern African, 30% Arabian, 23% Omotic, 8% North African
Somali: 42% Eastern African, 30% Arabian, 19% Omotic, 9% North African
But don't think of that as "Somalis came from the Muslim invasion". I'm pretty sure that Arabian admixture has nothing to do with Islam, that comes from thousands of years earlier. Linguists see a movement of proto-semetic language into the horn of Africa in 800 BC, so a good 1500 years before Mohammed, I think the Arab admixture either comes from that event or comes from an event earlier time period. That would have predated the Arabic language but way postdated the Somali language which is indeed one of the oldest languages on Earth.
And I should point out that this is one of the best studies, but no study is perfect. This study didn't resolve the Cushytic genetic background in east Africa, but other studies have. So they say that right in the text, that there's likely a missing Cushytic element that wasn't shown in their tests, and there may be other elements as well. More studies will come up with more refined #'s. But this is among the best information to date.