Inteferring in that duel was kind of dickish of MC. It was supposed to be 1vs1 and it's not like there were any real stakes, it was just for fun. If his friend wasn't strong enough and got killed then that's just how PvP works.
I'm surprised Edgier Kirito took it so well, if it were me and someone did something like that I would probably spend the next 2 minutes raging about it.