More or less the order is right, but perhaps Rum did not know how many people were in the room, so he decided to wait on it since he heard no scream. Rather than exposing himself, he would wait for a minute maybe while texting someone. Kohji, for his part would want to hide the mirror in his already messy room since it wouldn't make sense for a cut mirror to be on his body or Amanda's. So he tries his best to hide it by moving to his room, for it is the best option he could've think so in his state. Rum also knows about APTX way of killing, so since he is short on time and don't want to implicate another culprit is involved in the crime by using a tool that is not compatible with Asaca (Asaca perhaps brought his/her weapon and beaten Kohji with it, so using another tool would implicate another person. Hence it is best to use APTX in order to ensure nothing traces back to him).