It has nothing to do with the bezel
As you don't seem to be aware: active 3D TVs work by alternating their display between an image for the left eye and an image for the right eye. The glasses you use to watch 3D on these screens have shutters that alternately close in sync with the images on the TV, so all you see in your left eye is left eye images and vice versa. The speed at which this occurs is faster than your optic centres "refresh", so your brain gets a continuous stream of data.
What LG have done is devise a system where the "left eye" image is player 1's screen and the "right eye" image is player 2's screen. The glasses are then set up to close both shutters simultaneously, so each player's glasses only let him see images for his own game. The result is full-screen play for two players on the same TV.