Nobody should be amazed by this. There's not that much shooter skill involved here.
What we're not told is that he's been shooting that same target, from that same position, with that same rifle, same iron sights, 10 shots a day, two days a week, for 10 years. This feat is no different than that of those old West show cowboys who throw quarters in the air and hit em every time with their Peacemaker revolver or lever carbine, or that guy that shoots thrown plates with a bow from horseback, etc. They can do it every time because they've done it 10,000 times.
Put this guy on an unfamiliar barren range, no trees, no landmarks, with a giraffe gong instead of a bison or whatever that was, at the exact same range, elevation, wind, etc, and he'll miss the first 5 shots, probably the first 25 shots or more.
What we're seeing here is repetition skill, NOT pure rifleman skill.