Step a side
VIP
I believe that linguist was that Jewish student on Anthrogenica. The Cushitic influence in Arabia is real and it pre-dates the introduction of Semitic languages entering the horn which is recent. The latter I believe is an early Iron Age/ Late Bronze Age introduction while the Cushitic influence is from before the old south Arabians reached Yemen from further north.I think MSA would also be a West-Semitic subbranch. I recall a linguist saying as much. But, overall, Midas' point is that the substra in MSA and Ethiosemitic, whether they're specially connected or not, points to the possibility of Yemen originally being very Cushitic inhabited which archaeologically tracks because the Cushitic pastoralist artwork known across Sudan, Ethiopia and Somalia was also found in Yemen pre-historically so much so that it's called "The Ethio-Arabian style" by some.
Not to mention that Horner stelae culture also seems to have spread to Yemen quite early and that as recently as the Early Modern era Somalis and other other Horners had a wildly strong presence in Yemen (1.5 million+ Somalis before the war) which sort of implies to you how easy it's always been to be up there in strong numbers. His theory definitely has merit that Yemen was once a Cushitic stronghold before the Semites came in droves from the Levant and usurped them. Archaeologically and linguistically it almost seems a certainty.
Basically what I am saying in simple terms is that when the Semitic languages entered Eritrea there were already old south Arabian languages in western Yemen adjacent to the Red Sea. @Midas will have you believe that old south Arabian were not in Yemen yet when the Semitic languages were entering the horn which is wrong.