Medcare called me last night. Apparently they tested me for the obvious things related to my kidney cell/blood in urine episode and everything they could test for in a urethral culture came up negative. While it's some assemblance of an answer, it still doesn't explain why it happened in the first place. In any case, I'll keep an eye out for anything abnormal and hope that nothing is wrong or that I've just bruised my kidney somehow and that's why. I still feel very uncertain about all of this.