Over 1,000,000 Damage Mitigated in 1 Game... How Do?

In this game (https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2717368232/214990377?tab=stats), I played Kled. Not entirely well, but I'm new with him, so I reserve the right to suck.

Anyway, I built a little damage and then went tank (as one does). I thought nothing of it until the very end of the game, when one of my teammates brought my "Self Mitigated Damage" stat. I apparently mitigated 1,132,240 damage in that game.

HOW? What? There wasn't that much damage throughout the entire game?