I don’t know how Windows games are counted when they are executed in a Linux environment but I do know that Windows games executed on macOS through GPTK are counted as Windows environment, which is dumb.
Anyway, good to see Linux holding strong. I’ve been waiting for this since Hardy Heron
The steam survey doesn’t count individual games; the Steam client itself collects and sends the data after prompting the user for permission. So all the matters is the OS visible to the Steam Client.
Which is, in that case, Windows 10 in a Wine bottle.
Steam.app can’t run Windows games directly on macOS, like it does on Linux with Proton. So you have to install the Windows version of Steam in a Wine bottle to be able to install and run Windows games from Steam on macOS