what do you suppose Azar's reaction to the boy means?

Azar gives a bar of chocolate to a little boy with a plastic leg. We can surmise that Azar feels badly for the boy. This is just one of many random "nicer" memories that O'Brien shares of war.

It's O'Brien showing that Azar was a compassionate person, he just hid all his emotions to get through the war without losing his mind. He had to harden himself so he could make it home. However, he had a weakness.