Can LCS Thresh Relic Shield AutoExecute?!?

I am watching an old Game1 TSM vs IMT. 30:25 in, Thresh kills a minion with 50% health. There was no Rend or anything, watching on 25% speed. He literally just does 50% damage when Kalista is only doing like 10%.

I have seen them actually do real last hits. It makes no sense for the pros to need a handicap. I was just wondering if anyone has seen some wierd executes. I will simply be more alert to it.

At 31:25, Thresh does not execute. But does like 40% damage with an auto. I guess he just does a ton of damage.