Let’s give the artist some credit for being clever. “Easy come, easy go...” regarding a lost balloon, or your money. Very clever. As for shredding the girl and not the balloon, that is a much darker message by the artist.
I thought maybe the battery died.
I wonder if he rigged it to trigger with the sounds of a finished auction, or if that would be too much probably easier if he set it off remotely, but more problematic because he’d be destroying someone else’s art at that point, whereas if they bought a painting that was already rigged to destruct, that’s what they bought, even if they didn’t know it.