This clip of a song titled "Swahili Bina Adamu" has mixed voices with a two-stringed,bowed instrument called a rebab. The vocal technique and the accompaniment is distinctly middle eastern rather than African.
The island of Zanzibar, off the east coast of Africa has been thoroughly Islamized. The Swahili, who lived here are traditional seafarers. Their contact with the mainstream Islamic culture to the north is very old. The Islamic influence can be heard in the music.