That means they are not actively blocking it, not that they are contributing something to it. For instance DLSS 2 support was enabled by Nvidia offering the missing DLL file for use in Wine. I'll have to look what "support" entails in this case...
Found this:
https://github.com/jp7677/dxvk-nvapi/pull/213
So it's another case of a Windows library file passing data to the Nvidia closed source driver doing the actual work, contributed by an Nvidia employee. So not exactly Valve's work, nor actually open source.