First he bragged about iPhone 7 Plus's cover, it's supper tough and all that but at the end found out that Galaxy S8 Plus is more tougher than iPhone 7 Plus. He thinks the bend point of iPhone is where the sim card tray is. Although that is quite week point but I think he put more pressure on that point that's why it bended. Otherwise you can clearly see where ever he put a bit of pressure he just ripped it off, as you can see near the camera.
As per this experiment we can say that Samsung Galaxy S8 Plus is more stronger than iPhone 7 Plus.