[mmanfrin]

Actually I think what you're referencing is still Dunning-Kruger: "Conversely, highly skilled individuals tend to underestimate their relative competence, erroneously assuming that tasks which are easy for them are also easy for others." (from wiki)

[rithmoflife]

More specifically, it's the Downing effect: "One of the main effects of illusory superiority in IQ is the Downing effect. This describes the tendency of people with a below average IQ to overestimate their IQ, and of people with an above average IQ to underestimate their IQ." (also from wiki)