9 years is a long time. I'm sure he's removed enough from the experience to be able to laugh about it.
Probably should add to that " and he destroyed it in a way that did not harm the reputation of the artist".
This was in France, which has some strong moral rights for artists, including a right to respect of the integrity of their work (droit au respect de l'intégrité de l'oeuvre) which prohibits modifications and mutilations to the work that could harm the reputation of the artist.
I also found something that suggested that in at least some countries the right to respect of the integrity of the work requires that before destroying a work you have to offer to let the artist take it back, but I don't know what countries that applies to.
Granted, if you twist my arm I can come up with grand statements about oeuvres and the conversation between the art and the environment in which it is embedded bla bla bla, but that's just a way to justify the inflated price for something which is just kinda neat and fun.
He had the right to destroy the work since it was his and in his property, but to then whine about it just because he learned of its monetary value... It's just wrong.
Pfft, and calling it a "work of modern art" after the fact.