You don't need thousands involved. They told the students they were going to do a drill with blanks. The students couldn't tell if it was real or a drill until the police and media told them it was real. They were basically in a drill, and then lied to like everyone else. You only need a handful of first responders, hospital personnel, actors, corrupt sheriff, and the usually corporate media personalities. It's not as grand of a scheme as you'd think. They just control the majority of media to control the narrative and for damage control.