I don't know anything about U Chi specifically, but here are some general observations about medical school admissions.
Every year ever school says they had a lot more applicants than the year prior (at least this has been true for the last several years, and it is not surprising as overall applications have increased and it appears students are also applying to more schools). A class being full with no waitlist movement is really a reflection of how well the school planned the number of acceptances. Remember medical school classes are small, only 80-180 students typically. If even 20 students do something unexpected (family reasons, silly rumor on SDN, etc) then that can create a crisis for the school, either they have to figure out a way to get some students to defer or they have to go deep into their waitlist. It is a difficult balancing act.