You misunderstand the "No True Scotsman" fallacy to apply it to this situation. There's a metric for success (graduating), and no one claimed that the only possible way that someone didn't make it is "work harder". I said that perhaps that's the reason since by the time people make it to medical school, they're on a fairly even playing field.
NTS is typically applicable when someone expresses a goal like "being a good Christian" and then continues to redefine what that means, never admitting that some are good Christians because of endless redefinitions of the metrics.
