Yes, "hog" is slang for penis. Telling someone to "post hog" is a particularly common expression among more... online leftists. A degradation of their character, basically telling them that their opinions are worthless so they had better have a large member to make up for it.

If you search twitter for “post hog,” the very first result is a person sharing a photograph of their erect penis.

I assume they are converted Muslims who observe the Quran.