You have a point here. Perhaps a more appropriate statistic would be one that shows suspensions and expulsions by race on a school by school level, and see if and how well that rate follows the racial makeup of the school.
I'm fully supportive of the idea that entrenched, institutionalized racism exists and has even gotten worse in the twenty first century. That said, I'm a stickler for using the appropriate and relevant data to support the argument, in order to make it all the more unassailable.
I'm sure that a similar county by county graphic of black graduation rates would be very interesting to place over this map of black population. My bet is that there's a real correlation- a negative one. THAT'S institutionalized racism.