In my view, self defense is a legal defense when somebody used violence to defend themselves against an immediate threat of physical harm. I don't see how, legally, you could expand the parameters to fit this case. But I'm also not a lawyer.
The argument it seems to me you could be building here is that the victim of despicable bullying, ignored and misunderstood by all the authorities, lashed out out of desperation. And that in itself is an act of self defense. I think that's a moral way to look at it, but not a legal one. The latter will look at this exactly as mitigating circumstances.
You clearly have a different take on the situation. A bunch of dipshits showing deepfakes around on a bus, ostensibly with other people around who are not party to this dispute and a grownup in the driver's seat, does not convince me that even your interpretation applies here. But neither one of us was present, we are both arm chairing this, we are just sitting in different arm chairs. Let's leave it at that.