The video circulating online was shot by a camera near the teaching building. The camera was somewhat far away, and its quality was even inferior to that of some street intersection surveillance cameras. You could barely make out two women in the footage. Many people had to rewatch the video several times to roughly understand what was happening.
With such a resolution, it was already good enough to see what was happening, let alone identifying the faces of the individuals involved.
So, in the comments and posts online, it was said that the rescuer was 'a student of Yanhua University' because the incident occurred there. The girl who was saving people in the footage seemed to know martial arts; her physique looked very fit, her movements were nimble, leading people to infer that she is around twenty years old.
When the public opinions heated up, no one revealed the real identity of the purported rescuer, presumably because those privy to such information kept quiet.