It is hot air, why do you think it didn't melt until he broke it in pieces?. Hot air is in the trench based on how convection works. Not just vaporizers, but in general When ever you heat ANYTHING up, you will get some sort of convection of the air. They might not need to grind, but you would get WAY BETTER results if you do. Air is very light, and goes where there is less restriction, so if you use one big piece of herb or concentrate, it will just go around it. When using a concentrate this effect is even stronger due to being more dense then bud. When you break these things in pieces they hold more heat, as well as have more heat come into contact with them, which is why you saw the results he got.