All you need to know is that the dude used some keys, a knife, a razor blade and some other knick knacks and rubbed them on the screen. The screen looked fine afterwards.
The take away point is that glass will resist scratching, but is definitely not scratch proof. A lot of people watching this video decided not to put on screen protectors and now lament the scratches they have on the screen because they didn't realize that even though soft metals like keys and low grade steel won't scratch glass, sand and other things will.