Really weird bug - Got me firstblood - How?

So it was this match: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2267804018/220235210?tab=overview

Here's what happened:

I'm Jax top vs Yasuo top. Around level 1 I dropped him to about maybe less than 100 hp. I'd say around 50. I had corrupting potion ticking. He was around his tower, he leveled up, he also had his shield recover. So he leveled up and hit maybe 100-125 hp. I was around the minions towards the center of the lane, he was around his tower. Then he died. Sadly I don't think Replay.GG recorded this.