My understanding is that fish are relatively high in omega-3 fatty acids. I believe they’re important in neuronal function and cardiovascular function. Regardless, the media took the 2 facts and conflated the two to say that eating fish = lots of omega-3 fatty acids = good neuronal health = become smart

You’ll find that the media does this quite a lot - they take reputable scientific research and extrapolate it so far outside its intended use case that the resulting news report is complete garbage