We try and stay away from giving the message that pushing is ok in any circumstance. If something happens he's not happy with I encourage him to tell me.

On the other side, my son is rough. He's stopped biting but he still pushes. He could have been the boy you describe. But I'm a very different mother. I know my son is rough and am all over him like a rash, especially out in public.

I would probably have spoke to the child's mother rather than teaching your son to push him back.