Statcounter works by collecting and processing user agent strings from browsers accessing sites that use their analytics. Unknows OSes are probably the ones who don't give that info.

My guess is click farms with some unknown custom made os that skew that data?

That also might be a source of Linux users hence the relatively high market share of the OS?

Not to mention that India still has a lot of call centers (some for scams) that may use Linux because it's free (compared to a windows license)