The person you are responding to doesn't say anything about Chrome. WebKit can be built on Windows and Linux and there are browsers that use WebKit that support Windows and Linux.
It might be relevant to the assertion that WebKit is ubiquitous though, since the most popular browser using WebKit on Windows is Chrome, if say Safari on Windows gets less support because "there are other WebKit browsers," that it's not even the same WebKit in Chrome, but actually a fork.
It's possible the person didn't say anything about Chrome, or since all of the direct responses reference Chrome, it's also possible the parent comment was edited.
Yeah, I know. "Ubiquitous" is a bit exaggerated. But now there's enough WebKit users out there that developers can't afford to ignore them; especially on mobile, so the strategic importance of Safari for Windows is diminished.