Dunning-Krueger is commonly understood to mean that incompetent people are too incompetent to realize they are incompetent. But its lesser-known corollary is that competent people assume everyone else is just as competent as they are, and thus they don't have to explain anything. They can just start talking in the middle and use jargon, insider, slang, etc. Just like here, poster assumes everyone knows who "Cambridge Prof" is.