Yeah I feel like HN is being Reddit-ified with the amount of reposted clickbait that keeps making the front page :(
This study in particular has made the rounds several times as you said. The study measures impact of 18 people using ChatGPT just four times over four months. I'm sorry but there is no way that is controlling for noise.
I'm sympathetic to the idea that overusing AI causes atrophy but this is just clickbait for a topic we love to hate.