I saw the "stroke" and expected a fluff, but didn't see any double hit. Quite frankly, if you can extend a 2" (or whatever) back swing through the sand, continuing the momentum of the sand and the club without a double hit, it is OK under the rules. Think of a highly talented boxer's jab, which starts at 2" (or whatever) from the chin, and it can be accelerated through the landing of the punch and only slightly attenuating the force through the fist and the glove.
Maybe that's what happened to Sonny Liston (the ball) and Muhammed Ali (the club) at Lewiston, Maine (were you there, Michael?)? I saw that happen in a theater in the Bay Area, with a future NFL Pro Bowler Linesman as a part of our posse. He nearly killed the ticket seller after not getting a refund. Maybe he was wrong, and Ali that talented.....