I have been a linux user for more than 20 years and personally I prefer it over windows.
But according to steam statistics, 96% of its users use some version of windows (from 7 to 11), while only 1.47% use linux.
The OS is linux, so it should show up as a linux computer.
The steam client allows you to run games that only work on windows using proton, but steam runs natively on linux and if the game has an executable that works natively on linux it will install that version.
It's not that steam runs on this abstraction layer, but that steam can use proton to run specific games (Those that only work on windows)
There is not much difference with using any computer with linux and having steam installed on it.
No it might not. As I just checked, that is not an actual real usage statistic, it is a survey with answers given by participiants. Should you exclusivly use that steam deck, you might not even be aware that it is Linux ;-)
If you have a Windows Gaming Machine and buy yourself a Steam Deck, what would you answer...
That is not right. You don't answer anything, the only question is if you want to participate, if you answer yes, the steam client automatically captures all that information.
If you have a PC with windows and a steamdeck and you participate in the survey on both, the system will add a computer with windows and a computer with linux.
More than once, steam has asked me if I want to participate, and you shouldn't answer anything manually, precisely, because then the data would depend on your knowledge of your hardware.
EDIT: Maybe you are confusing some other type of survey, please, search on how the official steam hardware survey works and you will see that what you say is not correct.