I really don't want to comment too much on the incident as there are so many things that could have been the reason for your DGS's behaviour. I would say that he does need to learn about being hurt and causing hurt, but I would also say that children learn best about these things by example. Children who get lots of hugs and love tend to behave in a similar way to others. I am not suggesting your DGS isn't but I don't like the posts on here that seem to think he must be strongly reprimanded for his behaviour. He should be told it isn't the way you would like him to behave and then forgotten. I always like this poem
Children Learn What They Live
By Dorothy Law Nolte, Ph.D.
If children live with criticism, they learn to condemn.
If children live with hostility, they learn to fight.
If children live with fear, they learn to be apprehensive.
If children live with pity, they learn to feel sorry for themselves.
If children live with ridicule, they learn to feel shy.
If children live with jealousy, they learn to feel envy.
If children live with shame, they learn to feel guilty.
If children live with encouragement, they learn confidence.
If children live with tolerance, they learn patience.
If children live with praise, they learn appreciation.
If children live with acceptance, they learn to love.
If children live with approval, they learn to like themselves.
If children live with recognition, they learn it is good to have a goal.
If children live with sharing, they learn generosity.
If children live with honesty, they learn truthfulness.
If children live with fairness, they learn justice.
If children live with kindness and consideration, they learn respect.
If children live with security, they learn to have faith in themselves and in those about them.
If children live with friendliness, they learn the world is a nice place in which to live.
Copyright © 1972 by Dorothy Law Nolte
Oh and in my experience little girls are better at making the required responses than boys are, but they are also better at doing quiet, unobtrusive things to other children whereas boys do things much more obviously.