>>515296467 (OP)
To be fair, they don't really know what happened. From their perspective a person with a red hoodie stood up and made some motions next to the person in front and then walked off. This happened in their peripheral vision when they weren't really paying attention or expecting this. It's likely most if not all of them didn't know he had a knife as it was a small pocket knife obscured from them. Then after she just kinda sits there like she got startled.
Fleeing after the scene is simply self preservation once they realize what happened and the crazy guy is still on the train and might turn around and attack them.
You would do the same if a crazy white hobo stabs a black person and is still on the train walking around with a knife. You would gtfo of there before he turns around and comes for you. It's highly unlikely you would have shown great concern for the injured black guy.
I know you guys are autistic so it's hard to recreate the experience from the mental and visual perspective of someone seated in the train at that moment. They didnt have the eagle eye perspective of the cctv, nor did they have foreknowledge of what was to happen, and the hype on social media, unlike you autists sitting at home in your comfy seats. For them, it was a new real time experience and this is how they coped with the limited information they had to work with in those few seconds of whatever information from their environment entered their senses to be processed on the fly in order to make a snap decision response to the situation as they understood it in that very short moment in time.
The white people on this bus immediately left the bus when the Asian guy started stabbing the white guy, and they blocked the doors so he got trapped inside and then the Asian guy decapitated him