It's not a bug, Fares. It's literally a kill btw because the one who shooted your rustler last time will get the kill.
For example, I was in a rustler flying and you're a cop, you shooted me because you thought I was trying to kill the President. When you damage my rustler many times even a little bit with M4 or Sniper, you'll have that kill because you are the last one who shooted and damaged the vehicle I was driving.
I've done that many times to all rustler users, and if they crashed, exploded or too late to eject the exploding plane. Of course, I'll have that kill and I'll give an example too like a video.