Chinese undergraduates, what's wrong with your social communication skills?

Several years ago, I had an experience living with three Chinese undergraduates. When I moved in my new room, on the first day, I knocked their doors and said hello to them. They seemed introvert and a bit rude. However, considering their age, I found it normal. After all, it was their first time abroad.

During the following months, I proactively went to chat with them and the situation began to change. I found they were not introvert anymore. On the contrary, when we talked about anything interesting, they always engaged in conversation more actively than before. I thought I had successfully rebuilt myself as an approachable person in front of them by putting extra efforts. In addition, I found an eccentric phenomenon that they hardly talked to each other going on underneath. Most of the time, they stayed in their rooms with doors closed. I never observed any of them asking help from others; maybe they sought it through Wechat or QQ.

People can chat with their friends any time. Is that the justification for the ignorance of people living around?