Damage Breakdown Showed No Killer [Gameplay]

I was playing Tristana this game and my last death was counted as being to Tahm Kench but when I looked at the breakdown for damage, the little dropdown menu thing, it showed no damage by Tahm and there was one column which was very glitched and listed damage from minions. When I say very glitched I guess I mean that it looked like a dozen minion damage posts had been copied on top of each other.

1. Attack Tahm with team while surrounded by enemy minions, without Tahm having a thornmail.
2. Die. I've not tried to reproduce this.