A developing personality

My sis-in-law's kids came over few weeks back. That's when I came to know little bit more of suhas's budding personality. She has a son, S of almost same age as suhas. He kept playing with suhas's toys and as suhas is not very possessive, he happily let him do that and silently watched from a distance. Now, the trouble started when S started to snatch things from him. First few times my sweet little boy was patient and let him do that. When he kept repeating this behaviour he got totally pissed off and started yelling and when it crossed his patience level completely, he came to me in the kitchen, prompted me to accompany him and gave a punch on S's face. He did that so quickly that I was not able to stop him. Initially I was not very happy and tried to lesson him, but then as time passed I was amused that he was clever to take me as his security blanket and did his thing. I was also glad that atleast he didn't inherit my 'forgive and forget' kind of attitude and know how to save himself from others stamping on him. Now I'm a little relieved that he will not let anyone bully him when he starts school.