Sounds like an Ekko who wanted an S but didn't get his. :)
Now, I found the game you are referring to on lolstarz.com and lol-mmr.com.
By the looks of it, Fiora got characterized as being a support in that game - in other words, you were dualling top and she got identified as a support by the position/rating system (i.e., less minions taken, more wards dropped, kills given to the other dual laner [you] as opposed to Fiora, was getting assists instead of kills, didn't die to the opposing laner that much, etc.). The AI for identifying who or what is a support is far from perfect. In short, you managed to grab more minions and kills and she was rewarded for letting you be the big bad beefy Ekko that you are. :)
I wouldn't sweat it if I were you. Hopefully you enjoyed your extra key fragment and/or crate as a result. :p