On the other hand, an individual that knows about linux, decides to download a distro, install it, and get to the internet probably is way more tech-savy than y

On the other hand, an individual that knows about linux, decides to download a distro, install it, and get to the internet probably is way more tech-savy than your average user. He is thus more likely to spend more time on the web and his browser / OS / hardware will be more "visible" in those charts.