That air horn trick is a classic for moving animals off roads without getting them used to handouts. Jakewhite has a point about the tough calls rangers face in real emergencies though. It's never as simple as the rulebooks make it sound.
Look, sometimes controlled feeding by pros is the only thing keeping a herd alive through a brutal winter. I saw park rangers do emergency feedings during a crazy deep freeze once, and it stopped a lot of animals from starving. That blanket "never okay" rule ignores those real life rescue situations.