It learns your patterns of speed, gas and brake inputs, etc... and it adjusts to them...
This is why folks who drive fairly passively and get the ECU reset magically think their car got faster (since the slowish driving style it had learned was reset)
It's possible you're experiencing this in the opposite direction.
Generally 200-300 miles minimum for the learning to have much impact... at 500 it should have a decent clue what you drive like.
But the car is always learning.... if the slowish driver had, instead of resetting the ECU, started driving aggressively, it'd learn that pattern of behavior after a while.