If he's from the UK, then obviously he wouldn't be referred to as an American, would he?
In the UK we don't really refer to the colours of people's skin.
We don't care. They're just people.
If, say, we really HAD to describe him to someone else, we'd just say that he was black, very dark-skinned, brown-skinned or whatever. We wouldn't mention 'African' because we wouldn't know where his ancestors came from.