For all of the people who don't seem to understand how Gorilla glass actually works, I will explain.
Gorilla glass has a surface hardness of 9H, while the metal objects have surface a hardness < 9H. This is why the metal objects don't scratch the glass. Try it for yourself and you will see.
Dust and sand, on the other hand, are both comprised of substances that have a surface hardness of >9H, meaning that they CAN scratch the glass. That is why your phone can and WILL get scratched from having it in your empty pocket.
P.s. for all of the people who deliberately watch these videos, then comment something to the tune of "OMG Y U DO DIS :( GIV ME THE FONE INSTED PLS," they do these videos because it gets them views, and it helps people see how strong Gorilla glass is. They aren't hurting the devices. Relax.