Their statement of Dunning-Kruger is overly simplified such as to misdefine it:

> The less you know about something, the more confident you tend to be.

From the first line on the wiki article:

> systematic tendency of people with low ability in a specific area to give overly positive assessments of this ability.

Or, said another way, the more you know about something the more complexities you're aware of and the better assessment you can make about topics involving such. At least, that's how I understand it in a nutshell without explaining the experiments run and the observations that led to the findings.