It's a cube law. The area of a sphere is 4/3pi*r2 so doubling the distance reduces the amount of light energy entering your pupil by the cube root.
Of course, the light reflected from the walls also contains substantial energy. You can get a sunburn of your eyes that feels like sand in your eyes and lasts 2 or 3 days. The same is true for not wearing sunglasses on a bright day.
I generally avoid looking directly at the light when I am within maybe 3 meters, and not for long then. At the distance she was at in the video, i would be ok looking for the amount of time she did. I can tack weld without a helmet by looking away as soon as the arc starts. I don't recommend this for others, of course.