Unless non-US numbers skew it more than I think, I suspect a whole lot of those respondents had a choice between honestly answering one of two operating systems, given the wording of the question, and picked Linux over the other one for whatever reason, despite not running it on their workstation. I'd be shocked if figures for the US, at least, were over 10% Linux, as far as what developers use on their main pays-the-bills workstation. Students might skew as high as 25% (though that's still higher than I'd expect) but I don't think SO selection-biases so strongly toward students that it'd be enough to push the figure that high all on its own.
Who takes the time to fill in the SO questions? Not the 9 out of 10 checked-out corporate devs that do the minimum to collect a paycheck. These are also the people that will tolerate anything central IT gives them, even if the mouse cursor takes 2 seconds to render on screen. I am not at all surprised that the group that cares about more than the job, the job that takes the time to respond to SO, is also the group that cares deeply about what they use for doing their job. So if 25% of them responds Linux, that probably corresponds to 2.5% actual usage. Not that important, BTW: SO selects exactly the kind of people whose opinion I want to hear about their tooling.
What's surprising here is how deep windows is sinking. They were at one point famous for their dev tools. The fact that WSL (i.e. it runs Linux stuff) is now considered one of their top selling points for developers is almost too incredible to believe.
Sure, there's the usual HN- and HN-adjacent bubble of not recognizing that like 80% of working developers are just showing up 8-5 or 8:30-5 (was actual 9-5 ever really a thing?) killing Jira tickets using Java or C# on their corporate Windows box on which they (gasp!) don't even have admin access, and I bet that does have some correlation with who bothers to respond to SO polls (mostly not those folks, that is).
At two companies I recently (within 3 years) worked (one fortune 500, the other eternal hopeful start-up), developers used Linux (Debian, Ubuntu respectively) on their desktops. On a third company developers had laptops running a mixture of Windows and MacOS (given preference), but development was done within (remote) VMs sporting Linux. All US based (HQ in Silicon Valley), for all product/production servers were running Linux. Frankly, unless you explicitly write desktop applications for Windows or MacOS, I'd be surprised if you're not using Linux.