There are lots of reasons apart from racism that someone could wind up in your shoes. Performance isn't everything...hell, it isn't even the most important variable in the US workplace.
That said, if there is a shortage of black managers that could explain it. Lots of companies want to keep up appearances and laying off the lone minority in management is practically begging for a lawsuit.
The truth is, sadly, you will probably never know what happened and why. Best to simply move on.