When the control rods are fully down the graphite tips are safely under the fuel rods. Then when you want to increase reactivity you raise the rods getting the boron out the way and putting the graphite in at the same time which is cheaper than separate rods. On the day the control rods were fully retracted something that was never really intended to be done. So when the control rods were dropped for a crucial moment the graphite tips were accelerating the reaction before the boron could get in the way.

Whenever the camera angle in there promo vids goes to the side a bit, a single plane of 2d video is revealed.

This thing IS NOT 3D! It is just a big transparent LCD screen with a white box behind it.