If you read the reoprt there were two reactions, 1 Ill effects caused by the original showing of the video 2 Mass effects hours after the first showing which are after the fact as the second showing was some hours afterwards and word may have spread. The others were seen the next day after the effects and conditions resulting were publicised and children had the chance to discuss at school.
The important thing to remember is that discounting the mass hysteria aspect still leaves children who were affected by the first showing of the video