I believe the fact that there was one shooter has been established beyond doubt. Otherwise, I would agree with your comments, and add that someone severely wounded or dying may make an involuntary movement/spasm which would attract attention.
In all fairness to the student who reported this (provided it's not a hoax, which is also possible, given the anonymity), when you've survived trauma such as this, it's common to relive it over and over in one's mind searching for reasons why you are still alive while so many others have died. As a result, some random event, such as another victim involuntarily distracting the killer, assumes an overblown significance.
We know there was one shooter. But did the kid’s know in the heat of the moment during all that confusion and mayhem know? Otherwise, I agree with what you said. I am certain the surviving student believes he was saved by the actions of the Muslim student. I don’t doubt that for a second.
I just think he is mis-interpreting what he saw. Maybe he will come forward with the full story of what the Muslim student said and did to distract Cho. Otherwise, I am flat convinced that the Muslim student moved involuntarily from his survival mechanism and not intentionally to save anybody.
Maybe we will learn more about this incident. My point is simple. The MSM won’t bother to check facts when the “hero” is a Muslim. They are going to go straight to press with the most glowing “possible” account, contrary facts notwithstanding. In this case, there are no contrary facts, just one lucky survivor’s confused opinion. But the MSM will make this poor dead Muslim student a Medal of Freedom winner if they can.