Problems with Mastery Rating

I just played a ranked game where my housemates were tripping the circuit breaker (RIP 4th or 5th series attempt) (shoddy wiring, moving here was a terrible decision, but there was nothing else available). Anyways, I found it quite strange I got anything higher than an F, given how little time I spent in game, yet I somehow got a C.

Ya might want to think about changing that.