Lifeline Warrior Medicine has a very simple technique for retaining your rifle on your back if you only have a single point. You hook the the sling over a vertical grip. It is a clever technique but it only seems to work with a vertical grip. Also the shooter is using what looks like a Magpul MS3 sling. As long as he has a sling point elsewhere on the gun, he could easily switch to a two point as the MS3 sling was designed to do.