Looking at the FAQ for the data source [0], specifically this part

> What methodology is used to calculate Statcounter Global Stats? > Statcounter is a web analytics service. Our tracking code is installed on more than 1 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.

I assume they infer the OS and stuff from the User Agent and other stuff in the headers of requests. And I assume scrapers collecting data for AI systems don't include the standard User Agent stuff Statcounter classified when they made their data collection tooling. So my guess would be non-browser-automation style scrapers that are getting around defenses and have header data Statcounter doesn't know how to classify to an OS.

[0] https://gs.statcounter.com/faq#methodology

Maybe windows users who weren’t smart enough to correctly answer the survey question?

Nevermind. These stats are computed by website visits:

https://gs.statcounter.com/faq#methodology

So I guess web browsers that obfuscate?