Does Manganiello actually DM at all, though? I've only ever heard him discuss the game as a player. I'm pretty sure he is not the DM of his home game either.
My understanding is that he does run his home game. He and one of his buddies were interviewed by Dan and Paul of Wandering DMs last year and talked a lot about Joe DMing, his plots and game style, their background with Palladium games including Teenage Mutant Ninja Turtles, etc.
It wasn't one of WDM's best episodes; ostensibly supposed to be about bringing old school sensibilities to 5E play, but Joe and his buddy mostly rambled a bit about their gaming history and interests. I suspect Joe wasn't 100% awake or prepared. But that being said, it was still a fun conversation.