Although not unthinkable, more likely, consider the effect of mental health, socioeconomic background, momentary stress levels, education level, etc that can influence both eating habits and cognitive abilities...

I'm not saying their hypothesis isn't plausible, their data just doesn't get us an inch closer to confirming it...

The organic vs non-organic argument is a false dichotomy anyway, so you got to be joking right?

Not necessarily. “Smart” people could be having very similar perceptions around being healthy whereas “dumb” people maybe don’t agree or don’t care or have a less homogeneous mind set. In other words, even if there is a causal relationship it could be reversed or not even have anything to do with being dumb or smart but around a third factor. Not to mention that this article isn’t about organic but about processed carbs. Also it says nothing about whether this is a long-term effect developmentally or just that it suppresses it temporarily and you bounce back to normal otherwise.