The article shows that the qualitative claim, that low scoring people tend to overestimate, and high scoring people tend to underestimate their ability, is nothing but a statistical obviety.

For the Dunning-Kruger effect to have psychological significance, you must quantify this, and show that they overestimate their abilities more resp. less than expected.

Regardless of how you set your expectation/null hypothesis, the absence of the effect would mean that the lowest scoring quartile would on average estimate their abilities to lie at 50% or below. It is found however that people in the lowest scoring quartile position themselves in the third or fourth quartile.

I'm not saying that this is necessarily deep or unexpected, just that the article only shows that the qualitative statement is true regardless of any psychological factors, and not that the Dunning-Kruger effect doesn't exist