You're assuming that they scouted this and carefully planned it to ensure they wouldn't cause damage. I doubt that.

This also assumes that the painting's protection is perfect. What if there is a flaw in the glass or a seam that lets the liquid get through somewhere? What if they accidentally threw the can while throwing the soup and it cracked something? Would you blame shift to the museum for not protecting their artwork from vandals properly? That would be ridiculous. I don't want to see every painting behind a glass case when I go to an art museum, either.

It's not worth the risk to such a artistic treasure just for attention seeking or 'awareness' of something totally unrelated. Last I checked Van Gogh wasn't part of the petroleum industry when he was alive. This kind of vandalism is stupid.

The should be doing shit like this to petroleum company offices.