Of course it isn't appropriate. But it wouldn't exactly have been the kid's plan-A, either. He will have tried other channels first (like raising it with teachers) and had a lack of support. Finally, he snaps.

We've seen this play out over and over with school shootings in the USA. Kid gets bullied. Kid gets no help. Kid gets a gun.

This is the same thing. Is it an appropriate response? No. Have we still failed him as a community? Yes. This bullying should have been dealt with months if not years ago. Clearly, it wasn't.

[Defence lawyer] told the court the child had been threatened and vilified on a range of platforms.

“In the past two months, it’s escalated in violence in terms of specific racial attacks against him at school,” he said.

Magistrate Mark Howden described the messages as “threatening and racist”.

He ordered the child be released on bail with conditions.

That tells you that the magistrate doesn't think the kid is a danger to the community.
There are no winners in this picture. The kid won't be going back to that school. Good odds he will never go back to any school. So this has likely affected him for life.
The injured kid is also probably not going back to that school. He is also probably going to be affected for life.

You're speaking as an adult. Guess what this kid isn't