Yea, Joe can lean a bit towards BJJ. But he mostly always gives props to fighters who are doing well regardless of the style. It's not like he doesn't gush over good strikers just the same.
Also, the ground game is something that is not really appreciated by the masses, so it makes sense for Joe to get excited about anything decent that happens down there. In truth, if it wasn't for Rogan, I wouldn't recognize half the shit that's going on. He's essentially promoting the part of the sport that needs promoting the most. Nothing wrong with that in my book.