What gets you an S rank, exactly?

I just don't understand how I got an S in this match. If anyone deserved it, it was Teemo. I know not many people play ADC Kennen bot lane as much as I do, so maybe that has something to do with it? I just don't know...

Here's another recent game I had as comparison: http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2475713895/229106060?tab=overview

P.S: And no I'm not complaining about it or anything, I'm just deeply confused...