My first guess is the author is aggregating the numbers from either the distros download data directly or they are getting the numbers from some place like Distro Watch. You can even get a crude sense of the increase in new users if you hang out in a distro help forum. I check the r/Fedora sub on reddit a few times a week, (I run Fedora 42 BTW), and there has been enough of an increase in new users posting "OMG, I just ditched Windows and look at my shiny new Gnome/KDE desktop!" to be annoying to some people. It can be hard to find those posts from people looking for help with a problem sometimes.

What no one can say is just how long those shiny new users will stick with Linux or run back to Windows at a later date. My gut feeling is, if half of this new 5% sticks it's a major, major victory for all the distros.

A lot of it kicks back to companies as well. If every time someone interviews for a new job they are telling users they need to run their programs or even just the application for the interview from a Windows machine it pressures users into going back. I always see shit like that for stuff that is even just browser based. I prefer not to install zoom, teams, and such and just open in the browser, but ive run into companies saying their typing tests and other pre employment material only run on Windows. It's usually false, as I never actually have needed it to install Windows, but it sows doubt in people who don't want to take chances when they are already in a potentially tight spot.

The stats are from StatCounter which has this in their FAQ:

What methodology is used to calculate Statcounter Global Stats?
Statcounter is a web analytics service. Our tracking code is installed on more than 1.5 million sites globally. These sites cover various activities and geographic locations. Every month, we record billions of page views to these sites. For each page view, we analyse the browser/operating system/screen resolution used and we establish if the page view is from a mobile device.

So it's the percentage if web traffic (to sites that use this analytics service)

Ah so that should be pretty accurate then, because the amount of users spoofing their OS is likely fairly low, and I would assume would mostly be Linux users as well, meaning it wouldn't sell the data as being higher than it is, but rather possibly lower.

Also someone who uses Linux is more likely to use adblock and telemetry blocking features. The actual count is definitely slightly higher.

Does telemetry block that? If you go to a site like this, does it get your OS correct?
I figured you'd have to use the spoof features like in Firefox to get it to say something different. (Like telling it your chrome so it doesn't block your browser on certain pages)

What's my OS? What is my OS?

Help finding out what Operating System your running. How to find your Operating System version. Finding out if your OS is 3 2-bit or 64-bit. What version of windows do I have?

(whatsmyos.com)

I know in Cromite I can do some of it from here:

You can get the browser version. But as per OP StatCounter says this

Statcounter is a web analytics service. Our tracking code is installed on more than 1.5 million sites globally.

I am assuming these are some extra js files or external scripts that the website will try to load, it won't be part of the native website itself. Adblocker will completely prevent those file or websites from loading in the first place.

My initial point might not be quite right though, in the sense of Linux might be higher by pure numbers but not by percentage. The sheer number of people using Windows, even if a small portion use adblocker could outnumber the Linux users.