I took this as more as poking fun at Calvin's common theme of superficially imitating "high art", opaque writing styles, and so on, in a very self-aware or cynical way, as a grift, since that's just what Calvin always does -- E.g. in the comics where Calvin sets up a lemonade stand, it superficially imitates a business, but is really just a scam.

An alternative or additional interpretation of his "curmudgeonliness" would be these are intended to tie into his bigger theme of critiquing those who gate-keep "high art". It's been a long time since I read any of these, but I do remember his biggest bone to pick wasn't with abstract art or anything in particular, but with the perception that comics / "graphic novels" could never be considered "high art". So, having his kid scribble some nonsense and call it "high art" is a bit of a middle-finger to art critics who relegate his work to the "funny papers"

As bizarre as this sounds, I actually do think there are legitimate criticisms of the mid-century abstract art movement -- notably, the CIA's involvement. However, that is pretty off-topic here and I highly doubt that Watterson has ever made a reference to this!

Edit: I'm not necessarily even disagreeing you, I think all of this can be true at once