If you produce art with meaningful content you are prone to critisism from people who question the meaning, that has nothing to do with people being unable to enjoy the artwork. But She brought up the topic of spying so why shouldn't I question the way she deals with that topic?
Yeah, but some artists choose phrasing that may not be correct for the impact it has.
"Who's watching who?" strikes you easier and goes with the simplistic motif than "Who's watching whom", which feels stuffy and dampens the mood of the drawing. "Whom" tends to be related to high-class, where this picture has a more simple, fun feel to it.
That said, as a writer, I completely agree that people need to care more about literacy...