This was a good read, but i note the reluctance on the writer's part to disrupt his relatives notions of lily-whiteness and even the family record keeper insisted on privacy re family affairs.
That aspect is very similar to the euro-descendants in a book i read by Edward Ball call Slaves IN The FAmily. The book had a lot of historical data about slavery in charleston SC in the 1600's when rice, not cotton was the big money maker. HIs relatives too, became irritated by suggestions of black relatives and some were openly hostile to the book he was writing as they perceived it to be "family business"
I recall too, the family in the PBS Documentary Traces of the Trade about the euro-descent family who was the biggest slave trader in Rhode Island - how some of their relatives were reluctant to have their family's involvement with the slave trade made publicly known - and how they each insisted they had no wealth now
So all i can say is it looks like a great deal of the ethnic-majority in america really ain't ready to know their real roots. They'd fall over dead from a heart attack because for 100 years they've been saying they're related to George Washington on mother's side and Queen Elizabeth on dad's side with a splash of Irish or Native American along the way.
BTW, there are a set of euro Mazingos (with an A) in MS where i grew up.