Doing both normal speed and frame at a time, it doesn't look to me like the ball touched the cushion. Neither player had a problem with the call. Evidently, the call was obvious in person.
If you want to see what a cue ball on the cushion looks like, go to 6:36:19. The cue ball during the questioned call looks like it never got with an inch of the rail.
The call was correct, and the ref could see it well enough.
Bob, this shot makes me wonder whether there is a situation where the table referee can call for a second ref to watch the other part of the shot. Like what if this shot came up hill hill in the World Championship final? Especially if they don’t allow video review.