It goes beyond that. The Oglaf world doesn't seem to acknowledge sexual orientation at all. These two aren't mocking heterosexuality, but a very specific person as revealed in the next part, and neither of them are lesbians.
Even a comic that gets humor out of god disapproving of anal sex doesn't seem to imply that it's homosexuality that's the problem, but specifically sticking a penis up a butt that he just finds gross.
Mm yeah. Also I just remembered the skeletons.
I mean, obviously people are going to have preferences and some of the cultures are... Odd, like Kronar's people, so it's less that everyone's bi than that there's little or no stigma.