I wonder if "took courses" could be a stand in for "prepared heavily". It seems like people with all the other attributes might think they didn't need to study.

I wonder if "took courses" could be a stand in for "prepared heavily". It seems like people with all the other attributes might think they didn't need to study. People without them might think they did and took courses to "catch up". In my experience, preparation is the key driver of performance in these types of interviews. It seems reasonable that a person who took a MOOC might have prepared in other ways as well while people who didn't probably didn't prepare much at all (since watching a few Algo lectures seems the most accessible refresher.)