Strava calculates its own moving time, which is different from the total time you have the app running. While they aren't explicit with the calculation algorithms, the gist of it is that if you fall below a certain speed threshold (lets say less than 0.5mph) for more than a certain amount of seconds it "pauses" the clock. Its also very good at detecting doping (using a e-bike or other motorized vehicle) by simply comparing your moving speed to a weighted average all the cyclists who have done the segment. In any case, I'm sure people will find a way to game the system but the fact that your earnings are capped at $40/month and expires the following month really limits how much you can benefit from doping.