Essentially, there were a great deal of shots and bodies in an area, and I was walking through a smoke grenade so I was understandably tense, I saw someone walking towards me with something that seemed to be a weapon but wasn't, and I misclicked based on reflexes and the tensity of the situation.
Extra Information
I'd like to apologise for my mistake. I understand that it was a rulebreak, which is why I immediately apologised to the person I killed after I killed them. I'll be more cautious, and I will do my best to ensure that it won't happen again.