Oofta
Legend
One of the big differences they've mentioned is that because they are doing it for an audience now (as well as themselves), they have to be more focused the whole time than they were simply playing at home. And that has consequences ranging from being more involved with everyone else's character drama to fatigue that you can sometimes notice as their decision-making and focus deteriorate over long, stressful episodes. And you also notice this evolve over campaign 1 as they get more accustomed to the new play environment's requirements and expectations.
But that just means that they don't stop during the game to discuss the weather or whatever chit-chat comes up. If we all agree that we want to get through a lot in a session for whatever reason, we also have very little extraneous interruptions. I know when I'm at a game day or con where we have a 4 hour slot, once we get set up we stay focused on the game once we get going. It's no different.
So once again I see a difference in how but not what. It doesn't make it a performance any more than the fact that they're far better at acting. In our home game we are also acting as our PCs when we're role playing.