I always assumed that too, that these were African names or something, but apparently this isn't so. They are just made up. There is a certain "sound" to them though, especially the girls' names. I still think it must come from some where -- have been patterned, originally, on something -- but I have no idea what.
You can find some odd names for the characters at a "Renaissance" festival that don't sound at all like anything out of the Renaissance.