What's different about Barawa and Tunni's is that Barawa is a far southern town and it has strong trade ties to the Swahili coast south of them. The Somali groups that live there historically like Tunni/Garre have been spread out to cover the areas from Southern Somalia down to lake turkana and came in cultural-contact with a number of Northern Swahili speech communities who were migrating north. They left behind their cultural imprints and remnant groups in form of Boni and Rendille.
That's what sets them and the town apart from say Merka and Mogadishu whose urban population speak only a coastal Somali dialect. Because they don't have strong contact or trade tries with the Swahili coast or Swahili speakers.
Some more information on how medieval geographical writings corroborate and support oral Tunni tradition about their settlement:
About the towns bilingualism and Somali influences in Chimiini:
Some examples of Somali influences from the same book i showed earlier:
Aside from this, the town and Brawa society itself is organized and divided into Somali clan structure of qabil and lineages ''reer'' they call it ''reeri'' and Guurti(council of clan elders), which can be seen in Todobo Tol ''Seven Lineages'' that govern the town.