There are a few strange things regarding kill counts etc, the other night I was shot up in a dogfight but still flying and still in the fight, when a message comes up telling me I had been shot down, I then managed to fly back to base and land successfully and uninjured.
That is because kills are recorded on "death of plane". You'll also notice when a
plane is dead, it can no longer be padlocked or F2'ed...
...ocassionally, A kill message will come up shortly before an engine dies, as is what I expect you are describing.
And technically, what does it matter that some other pilot has a kill added to his record...you didn't die - you didn't lose your streak...whats the big deal?