Trynd Killing his own teammate

I was playing Jax top versus trynd. I got ganked by the opposing team's amumu and the both of them turret dove me. I died and the turret took its last shot at amumu and he died. But the thing is, trynd got the kill. I'm not sure how I could get a video but the attached picture is of the game summary where it says that trynd killed amumu and it shows that they were on the same team. Unfortunately this game was ranked :/

Please let me know what you can do for me and this bug. Thanks! Spartan9154