Not sure about the appearence thing, but i think i have an explanation as to why they're culture is so eerie, it being that we know very, *very* little about it all.
You see, most tribes rely solely on speech to spread their culture and beliefs to others, which makes them very likely to completely change over a short period of time. Because there's so many different african tribes and each speaks its own language/dialect - nearly none of said tribes' members knowing english - communicating efficiently with a significan amount of them borders on the impossible, this means that many of them have no way of sharing information about their culture with us: they can't speak diretly to us because we don't speak the same language, and they can't give us written records to translate because they never made any of those, so we can only rely on a select few tribesmen that were able to learn english and hope that they know about what we want to learn.
To me, that's why their cultures - as well as many others - come across as eerie, mysterious and spooky: we not only don't know anything about most of it, but we currently have no way of knowing about it. It's unknown and it's unknowable, and those two things scare us human beings in a deep and primal sort of way.