It doesn't just sound like that, it was used to mean exactly what you think well before PostHog was founded. I'm still not sure if that was an accident or the founders were in on the joke.

I am obviously incredibly ignorant (not that I’d normally think so — but here I have no idea!) but I can’t think of what this means.

Would you mind explaining please?

Grindr is a hookup app for gay men. "Hog" is slang for penis, so one might ask someone to "post hog" if they would like him to send a picture of his penis.

Hog is slang for human male genitalia. Given that, the company's name is an imperative command to share photos of such.