The guy he made the comment about isn't from Africa - he's Dutch. Intentional or not, it's reflects that "you're from Scotland, but where are you really from" attitude which is more than a hint of "you're not really Scottish in the way I am". It alienates people who have grown up in a country they consider home and that's why it's just a shite thing to say.
If you're going to make a comment / joke that can only apply to someone based on the colour of their skin, you've got to be sensitive to how it might be taken - especially if you are in a position of authority like he was. As Maurice Ross loves to do, sounds like he's opened his mouth without thinking.