Much as I (in common with most people in Poland) dislike Jarosław Kaczynski, if there were even one shred of truth to this nonsense it would already be very much discussed.
Indeed, the guy is an absolute master of playing with emotions and stirring the pot. That's the hallmark of a high intellect, not a low one. Furthermore, even his biggest political opponents have never accused him of having an impaired intellect.
Looks like a particularly ham-fisted bit of Putinist trolling.
All of their trolling is particularly rubbish. I've never seen a good piece of Russian trolling yet, apart from invading Crimea.