score:2
Well, as you point out, the term Bishopβwhich is ultimately derived from the Greek episkopos > biscop [Old English] > bishopβliterally just means "overseer." While it came to mean a leader over several parishes in many traditions, its more general meaning could just as easily be applied to someone who oversees a single congregation, which these historically black churches seem to have done. I don't think there's much more to it than that.