After school a child was playing basketball in the living room, and carelessly broke a vase on a bookshelf. The child hurriedly glued the pieces together, and scared he returned it back to its original position.
That evening, his mother found the vase had "changed", and asked him "did you break the vase?"
The boy had a bright idea and said "a stray cat came in through the window and knocked off the vase". His mother was clear that he was lying, but didn't say anything.
After sleeping, the mother took a chocolate bare from a drawer and said "this chocolate is your prize, because you used our mythical imagination to make up a cat coming in through the window, and afterwards you can write good detective novels."
Continuing, she gave him another bar of chocolate, saying "this is a prize, because of your outstanding restoration; the cracks are glued together almost flawlessly."
The mother took out another bar of chocolate, and said "this last bar of chocolate expresses my deep regret towards you. As your mother, I should not have left a vase in a place where it can be easily broken, and hope you are not smashed or frightened."
The boy listened, and ashamed he lowered his head; he never lied again.
Compared to a punishment, this is a profound reward.
I think I've basically translated it okay, and get the general mechanics of the situation, but I'm failing to see anything profound about this story: after all, the mother rewards him for lying, and seems to blame herself for him breaking the vase while playing basketball. It seems like he would continue to lie, after benefiting from it. However, it's possible I'm missing some subtleties here.
Question: What is the moral of the short story 三块巧克力?