This is kind of an interesting situation ngl. Well it is getting told around that you have to ask why someone killed someone else, but as you said its says in the rules that you are only recommended to ask and only if you scroll further down to see the invalid KOS reasons you see that you need to ask. Its pretty much a sitaution where the rules are conflicting with each other. I am just surpised that no one even realised till now.

I dont think he should get punished for it, because he probably got told that this is the way how this would be handled, but I think its also kinda unfair for this guy that he got punished even tho this conflicting of the rules still exist. I think the warn should get removed (cause its kinda unfair for new people that read the rules, see its recommended and then proceed to get punished just because they didnt knew better) and the rules should be reworked