From the close up views it looks like primarily forearm rotation (probably with some wrist too) similar to gypsy picking not only in number of notes per string but in the actual movement mechanic. What do you guys think?
I’ve also tried to dissect Benson and Dan Wilson but Cecil Alexander seems to doing less compound movements and is easier to see. Benson is particularly confusing with his picking from the elbow but still being a primary USX player.