What he did was stupid and very wrong. That bottle was thrown hard - not just lobbed onto the field. You can assume ill intent with how it was thrown.
I would say it’s mitigated by the fact that numerous Utah fans were throwing garbage onto the field and he joined in. He’s also young. I was a moron when I was 18 too.
I hope he gets a punishment that will correct his behavior and make him realize the consequences of what he did. Yet I also hope he can fully move on soon and be a productive person and learn from his mistake.