It's very good news for Valve, which is seeing their platform do well. And it's good news for users of other Linux distros in the sense that compatibility with Valve's Linux probably helps ensure support for them.
But it doesn't mean, I think, so much that lots of Windows users are moving to Linux unless they are abandoning their desktop for a Steam Deck. More that there are likely people using both a Linux-based device -- Steam Deck -- and a device running another OS.