I'm not a rated pilot, and I don't have much mountain flying experience at all. But that little cub only needs about 350ft to land and on some even less to take off. They can get real low and slow - making that kind of STOL stuff within it's capability. The pilot musta' known his business to make it look as easy as they did.
Though - I'da' been defecating masonry in the cockpit on that one no matter how good the pilot was.