[Taraz]

I don't think that such a fact necessarily means that Y must be true. It would be a small piece of evidence in favor of Y being true, but it wouldn't be overwhelming.

It could easily be the case that being smart would put you in a special position which would blind you to the factors surrounding Y. Perhaps you surround yourself with people with similar intelligence so you are insulated from the larger community and therefore hold certain beliefs. Or maybe society treats you differently systematically and this results in your belief that Y is true when it is actually false.

It could even be the case that this increase in intelligence lets this group to notice certain trends around them that most people don't notice, but 30% of them misattribute the cause of these trends to Y. So in this case, the fact that they were smart let them notice something unusual and they misinterpreted its significance.

The fact that such a large percentage of the "smartest people alive" do not believe Y should actually decrease the chance that Y is true unless it is a very complex and nuanced concept.