I have spoke to Kyber and he had informed me of what happened. You were given a verbal by him for breaking rule 2.3 NLR and soon after you killed him (2.2 RDM). We see no reason as to why the punishment should be removed. You also have to understand that even if it was crossfire, it still counts as RDM, here is the rule:
2.2 Random Death Match - In order to kill or harm another player you require a valid role-play reason to do so. Crossfire is not an excuse for killing people nearby where you are raiding or shooting.