"This stat teacher is horrible!" puzzle

So several years back (at at time CSN used Angel and not Canvas), I was looking over some of our adjunct faculty pages on Rate my Professor. As part of my duties as then lead faculty in Econ I did hire and schedule all of the part time instructors. For one particular adjunct teaching online there was one particularly bad review posted that included as evidence of how horrible this instructor was (as claimed), the fact the the "average grade in the class is a failing grade so that in itself tells you all you need". It was pretty evident from her post that she was among those who had failed. Mabye only half joking, I might have had the reaction that since she did not even recognize the flaw in her statement - maybe she really didn't deserve to have passed a stat course in the first place??

Any guesses as to why I am calling this a puzzle and how this might relate to the material we have encountered thus far?