Found this on a website comments area. Maybe this is why Korea got DQed...
"The rules of short track are very clear that the passee or lead skater always has right of way until the other skater (passer) gets COMPLETELY past them. You stated that Korea had already made the pass before making the incidental contact, which is not true. They had come up beside the other skater, but not completely past them. This made it their responsiblity to yield right of way to the China team. Even though contact may be incidental, if it is beleived to have impeded the progress of the skater with right of way, it is clear grounds for disqualification. It was very clear that Korea's incidental contact did just that."