TAS stands for Tool ASsisted, basically scripts pressing the buttons on the controller

On the right side of the screen each letter lighting up represents a controller input (l is left, r is right etc)

Each line represents a gamepad controller (virtual in this case). When you see multiple lines it means multiple controllers (I am assuming this, as later there is more than 8 contollers active which is strange)

Whats happening is a script running to glitch the game from the start into a certain state, beginning of the video until 1:40, then it looks like an exploit happens of the previous glitches in memory, followed quickly after by a massive data load that is the code for the pong/snake demos that follow.