The reveal comes from X user @ChrisMack32, who posted a video showing them unplugging a Super Nintendo controller – connected via USB – at one of the...
That team writes emulators that run directly on Nintendo consoles, so they would likely test it on development versions of those consoles the same way actual console games are developed and tested. Otherwise they would be testing a Switch version of an SNES emulator running inside a Switch emulator on a Windows PC that would introduce it’s own errors.
They don’t need to, they have their own studio that makes all their emulators called NERD: https://en.m.wikipedia.org/wiki/Nintendo_European_Research_%26_Development
Those emulators most likely have always worked on Windows since they need to be tested somewhere.
That team writes emulators that run directly on Nintendo consoles, so they would likely test it on development versions of those consoles the same way actual console games are developed and tested. Otherwise they would be testing a Switch version of an SNES emulator running inside a Switch emulator on a Windows PC that would introduce it’s own errors.