I thought the body language of the smaller kid was that of a smart-ass trying to prove something. The bigger kid gave him plenty of chances to avoid it -- it isn't like he retaliated after the first punch, or even the second one.
It looks to me like the little sh*t learned a valuable lesson, and I hope that the bigger kid, whose body language to me indicates that he was fully aware that he could cream, pulverize the little yapper the same way a St. Bernard could obliterate a chihuahua, but was inclined not to because of the unfair differences in size. The little sh*t, it looks to me, was taking advantage of the bigger kid's good nature and miscalculated.
(Regarding my post #30) ... or as your dad may have said, “the little cheet.” ;^)