The Dunhams were slave owners and the Luo tribe were slave traders. Here’s an article that discusses this: http://www.usvetdsp.com/jan08/obama_lou%20tribe.htm
I can envision the Obama dinner conversation date night, “Michelle, my Luo great-great-great-great-great-grandfather sold your great-great-great-great-great-grandfather to my white great-great-great-great-great-grandfather. Isnt’ that a coinky-dinky??”