Yeah i read about it a while back. It's a wacky story to be honest. Genoese merchants traversed the cape of good hope but never heard of again. Another genoese traveled to east africa in search of the lost genoese merchants. He traveled to habasha down to a country between two rivers probably mogadishu. He said that they had his own religion. He then traveled to zanzibar.
Remember zanzibar was not mentioned a lot at these times even ibn battuta didn't mention zanzibar but he talked about swahili coast, first to do so.