Well I think it is how the game detects the way a player is killed, you were in a vehicle when the player accepted his death the damage was dealt by a sniper rifle but at the very moment the knocked down player died you were in a vehicle so the game detected the kill as a Sniper Rifle drive-by.
I am fully not sure but this might be a samp bug rather than a mcnr bug I am afraid but I think there is no solution to it @Mike Can you give your opinions about this bug?
It's not actually the game killing the player. In fact, they don't die at all. Players only truly die from drowning, explosions, and fall damage I think. For anything else, their health remains at 1hp and a death animation is applied, then they are respawned. Although I do call the 'OnPlayerDeath' event, but it didn't actually happen. I remember the last player/weapon they took damage from. I had a basic check that said if the attacker is in a vehicle, put 'drive-by', but it was an oversight on my part that they might die after-the-fact like this.
Anyway, it's fixed next update.