it means that the written language of somalia was derived from arabic, i dont know what the official language of somalia is, isnt somalia just now creating a government, the new government has to decide that
i dont know about somalia specifically, but the arabs or muslims pretty much conquered north africa and large parts of east africa, and a lot the trade going on in africa was actually the trading of african slaves
http://en.wikipedia.org/wiki/History_of_Zanzibar
so the ships and ports of east africa dont really refute the point that africans lost because of technology