Not always. I once got accused of cheating at University because my take-home assignment was so much better than my in class work. At home there was no pressure to perform. I could practice and try things.
I once was accused of cheating as well, as my term paper was "too good". (Long before computers.) I brought in my cites (books) the next day and dumped it on his desk. He grudgingly changed the grade from F to A.
Nothing is perfect.