Speaking for myself, I suppose, I had a server running a much older version of Mac OS X (10.15) simply because I couldn’t update it beyond a certain point. Only recently did I finally install Fedora on it. Technically, I would be listed on this statistic as moving away from OS X to Linux. But such a huge market share for OS X vs macOS? That doesn’t make sense.
That leads me to believe it’s a matter of web browser reporting, and some report macOS as either “macOS” or “Mac OS X” depending on the browser, but they really mean the same thing.
I recently switched to Fedora after using PopOS for years. I like it because it’s just less… fiddly? Like, I don’t like COSMIC because it just doesn’t feel ready yet, and I honestly prefer DNF over APT. It has a very ‘set it and forget it’ sort of feel, which is great for a server.