Broadly: Typefaces are not copyrightable. Font programs, however, are.

So that's in the clear, which may be the point of the art.

I understood Stupid Font to be a comment on copyright.

My understanding is that the written form of the font is copyrighted - a redrawn version would not typically be copyrighted.

It's complicated so please don't take this as legal advice.

I think it's pretty clearly fair use. It's a parody, that significantly transforms the work and doesn't compete with it.