132-2-11: medications for athlete’s foot

The correct AC is A: The reporter concludes from evidence showing only that M can cure athlete’s foot that M always cures athlete’s foot.

The wrong AC E is what I selected: The reporter presumes, without providing justification, that there is no sizeable subgroup of people whose athlete’s foot will be cured only if they do not take medication M.

I can't eliminate answer choice E. Does this mean then that the answer choice is saying the author makes the error of assuming there is no group of people in the study who took medication M and were not cured?

And my question is how come this is not an error the author makes, because by confusing necessary for sufficient, isn't the author making the error of thinking there was no person who was cured that did not take medication M? (which is what I thought E stated)

I know why A is right, and I understand this is the right answer, I just can't seem to eliminate E and I think I am complicating it.