The deck is the god tier emulator platform: standard homogenous hardware including a standard set of gaming controls but still a normal PC running a desktop OS. People joke it’s a better Switch than the Switch.
That person made it sound like this is deck specific thing, which it isn't.
It's not even a steam thing.
You can play emulators on all sorts of computer devices hooked to TVs. Nothing stopping you from having corded or wireless joypads and controllers. Obviously that's not a replacement for mobile gaming. Well, I am just saying the opposite is also true. You can get your achievements.
No of course it's not a SteamDeck specific thing, hence why I started my post with "If you have a SteamDeck". As in, hey, if this interests you and you have a SteamDeck (or are considering getting one), here's some things I found useful.
That being said, I had no idea RetroAchievements even existed until I bought a SteamDeck, went through the EmulationStation setup, and got to the setup screen that was like "Hook up RetroAchievements?" and I went..."you can DO that? Holy shit!"
I've had emulators on my PC for years and didn't even know this was possible, as nothing ever let me know it existed before then.
Also while I've had emulation on other portable platforms over the years (and bought some dedicated hardware), I haven't had any portable hardware just work for emulation and work for such a wide variety of platforms as the SteamDeck.
I didn't even buy the SteamDeck with that in mind originally, and just a few weeks prior to getting it I was screwing around trying to get my old Vita set up for emulation with frustrating results (had to keep reinstalling something, never seemed to take), and then I checked it out on SteamDeck, and now I use it for emulation more than for playing my Steam library.
So… not sure why you’re surprised.