Following your logic, I could make an argument that this deserves less punishment since there is infinitely less physical damage. Most store owners that experience graffiti suffer the most from the fact that it is time consuming and expensive to clean up and/or repair. It is however trivial to delete these tweets.

EDIT: Additionally, seeing graffiti on a store may give me as a customer worry of going in for safety reasons, so their business could actually be hurt (aside from the costs of cleanup described earlier). The reality with this case is that I doubt anyone will draw conclusions about whether they will go to BK or not due to this prank, so the idea that just multiplying by eyeballs is a good metric is suspect.