Thats possible, tho it's usually the bream that wind up over populating. It depends on the size of the pond too, and it's age. If a young pond then the fish just haven't had time to grow yet. An old pond then I would agree with ya, just overstocked.
I fished a pond years ago that was in a back pasture on the persons property. Hadn't been fished in years...pulled crappie out up to 3 lbs. and bass over 6