Can't swallow this one at all.
Publicity stunt by Banksy and the auction house.
The picture was framed on the wall.
The shredder would have had to be installed within the frame, requiring joinery work, electrical cables, maybe a remote control sensor to turn on the power.
There would have to have been auction house workers and the auction house itself to be in on this to make it happen.
I'm not buying into this publicity crap at all.