as a ex-knife admin i would have done the same, there is a different between camping as a afk and waiting for people to come near you, so you can beat them and kill them and actually being afk, you are allowed to be afk for some amount of time if you have valid reason for it, and yes if you are afk and you comeback and see someone who is poking you with a knife or waiting around you, you have the right to kill him and its not camping as a afk, and yes i know people can abuse this but there for admins are there to judge who is lying and who's not, and i think its super obvious that you were lying because you were triggered, it doesn't take a genius to guess that.
on your other stupid point that you mention, I was only joking when I said whoever kills manatee gets credits, first of all you can't just literally break a role and say it was just a joke (a prank bro ?) do you understand why that doesn't work like that ? you can believe your actions and sayings are not a certain way but that doesn't matter as long as the action you are doing is harmful in this case against the rules a admin can obviously have that against you and no it doesn't matter how many people are on the server, rules are rules.
I can agree that manatee is a little too harsh on the server sometimes, but admins have bad days sometimes too, in my opinion he was definitely in the right in this case.