Hello, I was the staff member who authorised and conducted your PK.
When you are under gunpoint, you are automatically placed under FearRP (there are some exceptions to this, but not in this case). If you refuse to follow the instructions given to you while you're under FearRP, as you did and admitted to doing in the Staff Sit and this appeal, you are risking your Character's life. Because you died while breaking FearRP, you were PKed. Furthermore, you also stated that you died after starting a gunfight, which is also a PK'able offence.
To provide clarification on PK Guidelines and general rules, as I believe you have confused them a bit.
You were permitted to open fire on an active threat, and as they were pointing guns at you, they were in fact being an active threat. However, that does not exclude you from a possible PK but instead an RDM violation. That clause is there to give you an idea of situations in which you are allowed to shoot, and it would not be considered RDM.
Regarding the New-Life Rule, when you die, you forget the past 20 minutes of your life (unless it was a mass shooting in the open). However, others who did not die (like the ones who shot you) still remember the actions you took in those past 20 minutes.