Heel pushing can still happen even when the release is good. The two issues of ab stemming and heel pushing are separate.
With a poor release and ab stem, the skier will push off the downhill ski and cause a pivot to happen. This may appear kind of like a heel push, but I contend its a bit different, though it clearly results in steering angle and skidding, wanted or not. But the skier is not really pushing the heels in that case, they are pushing away from the ab stem and pivoting the new outside ski. Any pushing was on the downhill ab stemmed ski.
With a good release, no ab stem happens
However, even with a good release, the skier still has to roll onto the BTE edge of the new outside ski cleanly and in such a way as to not push the heels out. Many people do in fact extend too aggressively for various reasons, which results in a "heel push". The cure for this kind of heel pushing is to focus more on moving with the skis, getting the skis to glide forward, thinking about pushing the front of the ski into the snow to bend it, rather than trying to push out on the skis to bend them and doing so too much and ending up with a heel push. Also the lateral projection that many people make to move diagonally into the turn can easily be overdone in terms of the extension movement, resulting in a push away, or heel push.
Some people get in a rush to steer their skis into the fall line, even after a perfectly great release. Combining steering and carving in just the right amounts so that the skis turn into the fall line and catch up with the CoM that is falling that way, is very refined skill. Some people can't do it very well or even get lazy about it. So they are inspired to extend more aggressively and push their skis out there instead, which requires much less refinement of skill blending.
Another kind of heel pusher is the kind that ends the turns on the heels. To me that is not a heel push. Its just aft balance at the end of the turn. But this skier will get stuck into a place that the only way out is an aggressive up move out of the back seat.