"Nebraska is one of 32 institutions who have been honored by the American Football Coaches Association for academic achievement.
The organization honors all Division I football institutions who achieved graduation rates of 70 percent or better for the freshman class who entered school in 1998-99. Nebraska recorded a 77 percent graduation rate for the class entering in 1998-99. The overall graduation rate of the 94 schools who participated in the survey was 59 percent, and the median graduation rate was 60 percent."
Notice how in the Bowl Disqualification category he starts using the words AND/OR. So the overall rate of graduation could be 85% but if the racial gap is more then 15% they're disqualified. At least that's how I read this
Touchdown
Teams with at least a 50 percent overall graduation success rate, at least a 50 percent black graduation rate, and racial gaps of less than 15 percentage points.
First Down
Teams with overall and black graduation rates of at least 50 percent, but racial gaps of 15 percentage points or more.
Bowl Disqualification
Teams with overall and/or black graduation rates under 50 percent and/or racial gaps of 15 percentage points or more: