It's about the intention. Banksy's intention was to create art. The other guy's intention was to destroy.
You can see art in destruction if you want, but the guy's intention clearly was to vandalize.
Same reason why Jackson Pollock's pieces sell for millions and I couldn't sell the stain in my garage for a dollar. Even though one could see art in that stain (just like one can see art in nature) having a car with a leaky exhaust doesn't make me an artist.