What is wrong with Yi on TFT?

I can't be the only person who's seen this. Yi seems to do 6x more damage than he should, without exaggerating. I've gone against Yi's who had ZERO extra AD items and he literally shred thru a 3k health Mundo with Bramble Vest in 6 auto attacks while only having maybe 126 AD.

Why is Yi doing so much damage? And how? Because reading his kit/lore on his champion, he should not being doing anywhere NEAR as much damage as he's currently doing.