I agree he seems to blow a couple of strokes lifting the spine but in the slow mo you can see the spine has good contact deflecting the leather around it and trailing the edge on a flat strop. You could only do that on a verrry soft strop.
His strokes are actually straight tho the strop bends.
This is an old video I've seen a bunch of times but this is the first time I noticed how light his razor hand is. He does close his fist on the return stroke but on the push stroke you can see daylight between his fingers.