What's wild about it? It's one person, and they probably mainly use a Mac. If they used Windows, it would be Windows-only at this stage. I have lots of projects that only run on Linux. Clearly, if the project succeeds and gains tractions, the other platforms will come.
It’s the HN link description that’s confusing y’all then? Because the home page, where you clicked before navigating to the compatibility page, says they “aim… to be cross-platform” says nothing of that being the current state