even if they couldn't predict which team would get which costume, only the former council president knew where to get something that fit the description, meaning it would've been impossible for the other 2 teams to find it. also while the runners on each team were both 2nd years, the finders for the cooking and fashion classes were both 1st years, but the business class finder was a 3rd year, who'd have the most knowledge of where to find certain items, especially having been the previous student council president.
tl;dr: I call cheating on that crap