Traditional Theory: "The country was named Moçambique by the Portuguese after the Island of Mozambique, derived from Musa Al Big or Mossa Al Bique or Mussa Ben Mbiki, an Arab trader who first visited the island and later lived there."
My Theory: The internet has a habit of parroting what is reflected in Wikipedia. And Wikipedia relies on sources that don't cite any basis for their theories. This Arab gentleman named 'Mossa Al Bique' urf 'Mussa Ben Mbiki' has been cited by various sources to have existed anywhere between 7th Century AD to 15th Century AD. That's a rather long time band to be taken too seriously. In such a situation, it helps to look at an alternative angle. When Vasco da Gama visited the Island of Mozambique around 1498, he saw that place teeming with Indian traders from Gujarat. So isn't it possible for Mozambique to have an Indian origin? When I googled about Gujaratis in Mozambique, this pdf showed up. It chronicles the tale of Gujarati Hindus in Portugal. There is a reference in this essay to an Ambe temple idol that was supposed to have been shipped from Mozambique to Portugal. Considering how important the Goddess Ambe or Ambica is to the Navratri loving Gujaratis, is it possible for Mozambique to have been derived from 'Moksha Ambica' (the abode of our goddess)? This is highly possible as the Isle of Mozambique was famed for its gold. Could it have been that the Gujarati traders might have stumbled upon the gold and to thank their stars, they built a huge temple for Ambica? Someone should explore this train of thought. You never know what it reveals.