4 yr olds unkind behaviour

That's pretty much what I told DD - she is anxious not to have a raging psychopath on her hands!!! Interestingly I took 3 yr old DGD out today (lives much closer so I see her almost daily) and asked her what she would do if someone got hurt and unprompted she said she would ask if they were all right and go and get her nursery teacher - so maybe its encouraging and educating that works at this age.

Interesting quote off the internet:

"The capacity to truly understand what is going on in somebody else's heart and mind doesn't develop until a child is six or seven, but youngsters do have the emotional – rather than cognitive -- ability to pick up on another child's feelings and match them with their own"

The incident you describe has been part of the learning process and of the development of empathy. A lot of what passes for empathy in small children is probably more an awareness that they will be in the mire of they do something, before they understand why it is wrong.

I am sure that you will all be keeping an eye on how he progresses with this bit of learning and helping him to grasp it and internalise it.

Yes, he is too young to have empathy , especially for somebody outside his family circle. don't worry about it, children this age just parrot the word sorry. adults show by example what is right and wrong, so tell him that it's wrong to hurt another child and leave it at that.If he keeps doing it, then sterner measures have to apply.