Hello Namas,
I've looked over your evidence and spoken with Callum about this situation.
You did RDM Callum, and therefore you were slain. You should have asked Callum for his reason for killing the first person, as he had killed him for throwing an incendiary grenade, which is a valid reason to kill him.
Rule 2.7
"A player kills an innocent and had a valid reason for doing so."
As Callum had a valid reason for killing them, you killing him was RDM. This is why you have to ask for a reason if you want to kill them for it. You cannot know if they had a valid reason unless you ask.
As for the second person, you joined the gunfight as you shot Callum before he could identify the body.
Therefore you did RDM him, and Callum was correct to punish you, so this has been denied. I have spoken with Callum about his attitude during this situation and how he should have explained the rule better to you, instead of letting his frustration get in the way, which he apologizes for.