I think the "whipping of the sails" thing is to minimize snapping. I got some major snaps and twistage on Hershey's flyers last year, and the ride op told me that was because I was whipping the sail (which I don't do). I've also been told at Celebration City not to whip the sail but snapping was never explicitly forbidden. But that was before I knew how to snap. From what I hear, they will stop the ride if someone starts snapping.
However if you start snapping much in front of the snap nazi, he starts yelling at you to "settle down". I'd think the snapping would be much harder on the ride than the actual whipping of the sails. It's got to be a ploy to minimize snapping without saying snapping since many people wouldn't know what that meant and the ones that do tend to snap via other techniques.