No it's not the end of the World, nothing in this situation is the end of the World.
Tears can come with a lesson, but they didn't here.
All the kid was taught by Izzy was that 'might is right', not that there is a reason to carry yourself with class in the World.
Why would the kid regret doing what he did to Izzy now that Izzy did it back to him? Because it felt bad when he experienced it? That's a selfish motivation, as opposed to Izzy teaching him that what he did was classless leading by example, and the kid seeing Izzy is a good guy who didn't do it back, therefore feeling bad about what he originally did to Izzy.
Going tit-for-tat simply creates a bitterness, not a lesson.