Forum:Killcam Lag or Killcam Bug/Glitches

My younger brother told me that he was watching a video of call of duty killcams and in this video this guy shot this other guy in front of him and then in the killcam it showed the guy he shot was behind him. Now to the question my brother said it was lag and I say it was a bug or a glitch. Which one of us is right? I tried to find something on Google but I couldn't.