The "horde" of tieflings does make sense...They're a band of refugees from Elturel led by Zevlor to find a new home in Baldur's Gate. Their oppression as tieflings is why they're stuck out in the wilderness barely surviving off a few druids' goodwill.
As for the black characters...Rath and Wyll are the only ones I can think of that are black. Most of them are white. There seemed to be very few humans among the druids though.
