The cop seemed to be doing you a favor by "Dropping" your speed. Maryland cops have done this ever since I began getting tickets back in the 70's and probably before. EVERY speeding ticket I have ever received (less than 6, more than 3 but I can't recall exactly) has had its speed reduced.
The cop "seemed" to be doing him a favor? It was an enormous
favor, and he didn't have to do anything of the kind. Back in the day, I got two speeding tickets in Maryland, and both of them were for exactly the speed I had been driving, as near as I could tell. Maybe because I was driving a sports car
Keep in mind that one reason that cops drop speeds, when confronted with a reasonable and presumably safe driver such as this one, is to avoid any follow up, such as having it contested. I mean, who would?
The intent is to appear to minimize the effect on the driving record but in reality, the officer doesn't care if you are guilty of 9 mph over or 30 mph over.
Now come on. Try facing a cop after driving 9 over vs. him catching you at 30 over. In the second instance, there's a good chance he'll be mad instead of just bored. Outcome possibly quite different.
I still say he should follow one good turn with another. Attempting to 'game the system' after having been shown considerable forebearance is asking for it, and pretty questionable in the karma department as well.