That doesn't really answer Funt Solo's point which, and forgive me for paraphrasing, is that the Robin Hood film is a fantasy. There is little to no "realism" in the film.
In any case, the film also has a whole sequence showing how he ended up in England. The presence or otherwise of meaningful quantities of people of colour in medieval England is irrelevant to this. Even if the film was trying to be "realistic" which, just to be absolutely clear, its not.