The idea is that the motor control is pretty hard to program, and by using reinforcement learning, one only has to tell the computer whether it hits the right keys (reward).

The reinforcement learning algorithm takes in the state of the fingers and piano keys, and outputs the required motor actions to perform well.

Also, as you are too lazy to read an article but still feel entitled to comment on it, I herby give you -1 reward. Let's see if that helps to improve your character.