It's a really impressive display by Girardi.
How did a fan get so close to a news conference? Well, apparently in Chicago, they let fans who sit in the expensive seats right behind home plate go in and out of a different exit than the commoners in the rest of the stadium. And the entrance/exit is right across from where the news conference was held.
Here's guessing that fan won't be invited back any time soon, though a little good-natured heckling is part of the game.