The Dunning Kruger studies were observations, but I believe I have seen the term "Dunning Kruger Effect" used pretty often to describe the possibly/likely explanation to why Dunning Kruger observed what they did. Which is that once someone learns just a little bit about a complex topic, the effect is that they start to over estimate their competency in said topic.

If it were simply the idea that you don't know what you don't know, then you would expect to observe over confidence in people who know almost nothing about a topic. I believe D & K observed a sort of bell curve. (actual knowledge level on the x axis and confidence of knowledge on the y)