Hawiyas who were part of the wider Somali networks dominated the Shabelle river and farmed both sides of it along with the Raxenweyne. They followed the Shabelle down until they hit the coast which had red soil and hills. They named it Xamar after those red hills. Most of the economic export activity was in Harar, Zeila and most importantly Berbera. Eventually the intertropical convergence zone brought sail boats from India and Asia towards the eastern coast of Africa just as they had come to Madagascar (see malagasay in Madagascar and their Asian admixture). Some of these immigrants brought food and clothing influences as India was a textile powerhouse powered by samosas and Bismati rice. Eventually some of the Somalis explored the world as well (see said of mogidhsu, the red turban wearing Africans in the Indian courts, and proto somali linguistics influence in old Swahili). As these Somalis were returning to Xamar they needed a landmark so they nicknamed the city Muqdi(in this context meaning Foggy as there was fog from the cold ocean water meeting the morning star) Dishu meaning end of as the river shebelle and the ITCZ bring air towards this particular foggy zone allowing Xamar to appear where Merka and other coastal communities were obscured by fog. The Indian Ocean trade that spanned 1100-1700 till when the Portuguese messed everything up had Muslims in Egypt, Somalia, and Indonesia controlling the important waterways.
Proof;
-See the pre Islamic graves that followed other Somali graves appearing before the 1200s which is when the Reer Xamar graves are dated to.
-every writer that actually visited such as the chinaman that lost the war with the Persians and was enslaved until he left to the Arab traders in the area and even Greek travelers all describe pastoral people that constituted a majority in a coast where other Somalis would just kill all visitors; Only Berbera zeila and Xamar(mogdishu) were the trading zones allowed.
-Genetic admixture of Reer Cadcads/Xamar being limited to just one community on the coast, along with proto Somali influence on greater Swahili linguistics, see this paper;
https://langsci-press.org/catalog/view/192/1510/1623-1