Thank you very much! As audreydeux said, the core idea was to let the player create something over which they don't have control. The breakout aspect is mostly just an excuse for inviting to play with a musical system. I like to present the game as a musical instrument that doesn't produce precise melodies.^^ The bouncing of the ball is also here to make feel that the outcome is tied to rules of physics rather than the player will.
But yeah, I also agree that this is debatable. I wondered during the creation if "out of control" was equivalent to "loss of control". If there is nothing for the player to control in the first place, is it really out of control? And since in most games the music is not in the player's hands anyway, what does it really change for them if it is procedural or not? In a way if you play the game with no sound, it becomes just a breakout with too much randomness. Thus we can ask if the "out of control" aspect is part of the design or purely an esthetic…
But I guess that's why this game is often qualified as "experimental"!^^ I don't know for sure if it completely fits the theme or not, but it started from questions around the idea "out of control" that I tried to answer by creating an explorable system. And at least it produced something enjoyable! :)