I had to read that twice to get it. So the higher your AP, the faster it regens, because it has to get back to full from 0 in the same amount of time. So a guy with only 10AP vs a guy with 15AP, both spend all of their AP at the same time. From zero, it's like this:
If time for full regen was 5 seconds: 10AP guy gets 5AP back in 2.5 seconds, but in that same 2.5 seconds the 15AP guy gets back 7.5AP. After 5 total seconds, they each have back their max AP, so of course the higher AP guy has a faster regen rate.
Sound about right?