So.. I feel utterly stupid for starting this thread.
1. I was wrong about DAO showing few black people in comparison to DAI. I have absolutely no idea why I didn't really notice them before.
2. I was wrong about it not being realistic having many black people in Ferelden. I suppose it felt very strange to me at first as I'm a big fan of historical dramas, be it books or film, and those mostly take place in a basically all white England (whether that was the reality or not, I do not rightly know). You don't see a lot of diversity in a Jane Austen book, though, that's for sure.
But then again, as someone pointed out, this isn't actually England, and black people in Ferelden doesn't come from Africa, but places like Rivain where, as someone again pointed out, the religion and culture are very similar to that of Ferelden.
I take it all back. I don't find the diversity strange anymore as there are a lot of good reasons why Ferelden absolutely should be a very diverse country. Thanks for all the answers.
I really feel like deleting my posts, but oh well. Maybe someone else wonders about the same, and there are some very good answers here.
It's good when people can admit that they're wrong.
While Fereldan is based loosely (and it really is loosely) on medieval England, Why isn't Dragon Age culturally like England is kind of a silly point, when it exists precisely to be different to its inspiration.
Most of the people in the world are brown. White people, globally, are a minority. The fact that you found it weird that black people were present in a fantasy game shows how under-represented black people are in fantasy.
Bioware have given players the ability to choose their race, so if there were no black people it would be weird to be the only black person in southern Thedas.
There are several different tribes in Fereldan, the Free Marches, Rivain, who all have varying skin tones.
One thing is we don't really know how big Thedas is. Orlais must be massive - it has a desert to the west, lush forests, plains and snow capped mountains. It could easily be the size of a continent. And Tevinter must be even bigger.