Bleeding lower down the urinary tract. If the blood is present the whole way through the urine sample, and it is blood, then the bleeding comes from the bladder upwards. By far and away the major cause in young people is trauma ie getting smacked in the kidneys. Also not applicable. I think the most likely thing is haemolysis, ie the red cells bursting when they are in the blodstream.
Haemolysis can occur as an idiosyncratic thing to just about any drug - but is VERY rare.
It can also occur after very strenous exercise - because the red cells are literally burst in the soles of the feet as they get crushed. Used to happen after very long foot marches in the war. Again I think this is pushing it. I remain unconvinced that such a thing is happening at all - and would like to see this urine. If it is, it is potentially an important finding and needs to be documented.