It's somewhat unusual to get a speed reduced in the TVB, but it does happen - usually for an attorney who is a regular.
What happens is that the judge agrees to toss the radar or lidar out and go with the officer's speed estimation minus his tolerance. I am guessing that the officer estimated the speed at 25 over and the radar/lidar confirmed the estimation at 21 over. The officer had an accuracy of +/- 5 mph, so the 25 over was reduced to 20 over. Not too many judges will agree to this.
As was pointed out, points cannot be removed or reduced, and if there was another infraction with points within 18 months of this one the OP will be subject to a Driver Responsibility Assessment.