I still think it’s rather interesting as an approach. In fact with that, the potential of creating a DIY ND filter out of welding-glass [1, 2] becomes a little more unnecessarily involved :D.
Ha! This was listed in this 101 Science Experiments book(Pustak Mahal Publications) I had as a kid and distinctly remember being disappointed with it not working out as I expected.
It is not "cutting", it is "nibbling".
So this doesn’t seem legit to me. Cutting under water he’s just shaving pieces of glass of with what looks like a very different pair of scissors than what you have sitting on a desk at work. When he tries to do the same thing out of water he doesn’t angle the scissors like he did under water he heads almost directly towards the center. Not even close to the same actions .