Yemen is in the equation simply because the word Xawash itself is borrowed from the Yemeni Xawaij which is demonstrative of how they had a culinary cultural impact on us. This does not mean that Yemenis were the pioneers of the spices used in Xawash. Considering the historical contact we had with Yemenis, be it Somalis settling/trading in Yemen or Yemeni settlers in both North (Djibouti) and South Somalia, it is no surprise that they influenced our use of Xawaij. With the increased urbanisation of Somalis in the 20th century and the subsequent sophistication of our diet, we made Xawaij our own by refining it to suite our palate.
Human beings have borrowed from each other since time immemorial. Europeans were influenced by the Middle Easterners who in turn were influenced by the Indians etc. Even Indians and Arabs themselves were influenced by Europeans as exemplified by how tomatoes and potatoes became common in the New World thanks to European contact with Native Americans. Several curries, aloo paratha, aloo dishes are not less authentically Indian because potatoes and tomatoes were borrowed.
Some Somali diaspora born/raised nationalists, not you walaal, are bloody insecure and think an acknowledgement of an external cultural influence is Coonery. Proper Geeljire Somalis of old did not give en eff about the supposed 'civilisational' sophistication of others in regard to food, clothing etc. It is like folk want to create a historical and cultural narrative to inflate their fragile nationalistic ego.