I believe someone else already answered this question... (heh heh...)
As I understand what happened, when his backpack caught, he was at the very outer-end of the chair. He was drug around on the outside of the chair, and missed the bar (If there was one) because he was too far out. Next time you ride, check out the stop bars. Most of them are desiged to catch you if you are sitting on the chair, they don't reach beyond the end of the chair. maybe after this resorts will lengthen some them to catch situations like this.....