If BananaSlanger was T baiting then I don't understand why he'd warn you, but the rules do state this:
2.5 Valid KOS reasons
There are many KOS reasons and they all work in different situations and scenarios, here are a few; [You should question the player as to why they are doing these acts before you declare the KOS]
BananaSlanger was not directly shooting at you, rule 2.4 does not apply. Meaning you did in fact RDM, but as Banana was T baiting (or so you say) then the warning should be considered invalid.