They know him as the Haitian because hes black, simply put. Hell in company men in a flashback Thompson mentioned "We have a boy who can clear memories, we found him in Africa etc etc." Therefor hes African not Haitian. Show wise its probable they wanted to be politically correct to some degree and when Ted and Parkman were talking about seeing him Ted mentioned "he was... a Haitian" instead of saying "he was that big black dude" or "that nigger" or whatever else you want to say since even assuming a black guy is from Africa is racist now.