This video was posted back in 2013. The shooter, iainmcgregor8, sets up his bottle of beer in the cup holder of his folding chair. He sets up his rifle some distance away The beer bottle cap has a target attached to it.

Considering the bottle cap opener is affixed 90 degrees to the side, I suspect that it may be a twist style bottle cap. The force of the bullet hitting the opener would twist the bottle cap off rather than prying it up like traditional bottle cap designs.