Well not literally down to the individual.Not true.
There are so many Somalis who does not speak a word of Somali, does that make them non-Somali? Humans evolve.
A latino person in the US born to mexican parents that does not speak spanish is still Latino.
They are still somali.
But across Somalia, there are not and there have almost never been places were Arabic is spoken as a daily vernacular except by immigrants or descendants of immigrants(like the yemeni community in Somaliland).