As I understand 'Albion' represents Britain, but that could mean England, Scotland, Wales or Brittany.
It's hard to really compare these days, because back then it was more a case of sovereign states or regions than large countries ruled by one person.
For a long time, rulers and nobles of England were more French than English. And back then there wasn't really a France or an England as we would know it today.
Personally I think that if Arthur, or the person (or people) upon who he was based would most likely have been Welsh.