Okay well in that case the article is deficient (I skimmed it, assuming it was making the same case I already knew about[1] -- my bad). You can actually reproduce the DK graph without supposing that estimation bias depends on skill. There is an interactive visualization here[2] that does precisely that (click on the "line plot w/ centiles" tab). You can adjust the parameters to see how it behaves.

[1] https://news.ycombinator.com/item?id=31038386

[2] http://emilkirkegaard.dk/understanding_statistics/?app=Dunni...