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.