Yep, killing someone in self defense is a violent act. But it’s not a malicious violent act when someone else initiates malicious violence against you.I think you are confusing the "act" with the "person".
Killing someone is "violence". Regardless of justification.
Yes, that person can still be a "peaceful person".
But it does not change the fact that the act of killing was violence.
I think the guy thought that all he had to do is show the bad guy he had one too and that makes it a draw. But the bad guy won and he lost.