Why Thresh's Win Rate went up this Patch (Sorta a weird reason!)

I was wondering on this myself for a while, but finally after reading the patch notes again I saw this:

Bonus Armor Penetration: 45% -- > 35%

gains no armor per lvl, but the way things were coded, the armor he gained from his passive is counted as bonus armor. Thus, when champions got either of these items, they literally cut through 45% of ALL of Thresh's armor (barring his lvl 1 armor), instead of simply the armor he got from runes/items/masteries.

He effectively has received a fairly major buff to his armor, with no other changes to his items/kit. No doubt a tankier meta benefits scrappy champions like over many mage supports like , but it doesn't account for his win rate increase from 49 - 52-53%.