I think that's where he says "Dervish" by mistake. The Arbiter was called Dervish for most of development before Microsoft PR people made them change it, since the word Dervish is most frequently associated with a sect of Islam. Since the American-looking soldiers versus religious fundamentalists storyline of Halo was already a little awkward in the political climate of the early aughts, the name was changed to keep the comparison less overt.