Where's the proof that he was from Somalia then?
You're trying to change oral traditions that were passed down by your ancestors. There's a reason why they weren't forgotten.
Losing one's lineage is a sign of crumbling of moral society
Our ancestors lied because they thought claiming descent to the prophet will make them better muslims. On top of that they did it for political reasons to legitimise themselves over others. This isn't exclusive to Somalis even afar clans have similar bani hashim nonsense.
Sheikh Isaaq/ Isḥaq is an iffy subject and his genealogy is really all over the place, this one which might be known to many Isaaq clan members is his Arabian/ Hashemite genealogy:
http://anthromadness.blogspot.com/2015/06/the-interestingly-fraudulent-nature-of.html?m=1
shaq bin Ahmed bin Muhammed bin Hussein bin Ali bin Mudhar bin Abdalla bin Ayub bin Muhammed bin Qasim bin Ahmed bin Ali bin Issa bin Yahya bin Muhammed al-Taqi bin Ali al-Askari bin Muhammed al-Jawad bin Ali al-Ridha bin Musa al-Kadhim bin Jafar al-Sadiq bin Muhammed al-Baqir bin Ali Zainal al-Abiden bin Imam Al Hussein bin Ali bin Abi Talib
Now, this genealogy is completely impossible and frankly even mixed up because
Ali al-Askari, better known as
Ali al-Hadi has no grandson named Yahya descended from his son Mohammed. In fact the genealogy often doesn't even make much sense in the epithets it adds to these people. Muhammed "al-Taqi" for example was not the son of Ali "al-Askari" but his father.
Muhammed al-Taqi is an alternate way to refer to
Muhammed al-Jawad who was Ali
al-Hadi's father. In fact the
Ali al-Askari in that genealogy is supposed to be referred to as
Ali al-Hadi. "al-Askari" was used to refer to his son
Hasan al-Askari who was the father of
a boy named Muhammed claimed to be the great "Mahdi", this Muhammed in particular couldn't have been Yahya's ancestor either as he died as a little boy; too young to have fathered any sons.
However Ali
al-Hadi did have a son named Muhammed but he too like his nephew Muhammed (the young son of Hasan al-Askari) did die young (as a child) and is also by some sects of
Shia Islamthought to be "The Mahdi" / the final and 12th Imam in the place of his nephew/ he died way too young to have any sons let alone one named Yahya whom there is of course no record of anywhere.
This genealogy despite what I'm told about its "popularity" among some Isaaq clan members is a complete mess to be fully frank. All in all it's quite clearly fraudulent...
Sheikh Ishaq's origins as I said can even be a bit complex /
iffy. While members of the Isaaq clan will often fervently oppose this view-> the
Dir clan often claims that Sheikh Ishaq was essentially a member of the Dir clan and that the Isaaq are more or less an off-shoot of the Dir.