Yes and no, right. It would be an important distinction if those platforms were used for different games because then you could say "this increase in Linux is only on these platforms and those platforms only play these kinds of games". Maybe you could say that's true for the steam deck, but the way it and other handhelds are discussed it feels like people use it as a Generalist platform about as much as I would have figured it would be used solely for low intensity indie games.

But even if all new Linux users was steam decks, if they're being used as Generalist platforms then it would have the same impact as people switching to Linux on their PC because now every game is getting a signal that Linux is growing.

As someone who has both a steam deck and has swapped to Linux (and working on my friends to consider it as a fuck you to soul-less corporations) I suspect that although steam deck represents a large portion of the gains since its release, that it is not 90% of the gains.