I can't tell if this is what they're talking about, but I frequently stream from my desktop to a SteamOS handheld on my home network, and on pretty much any game that I can max out on my desktop's specs (Radeon 6900 XT, so not exactly the newest GPU, but it's able to do quite a bit), I can get 120 FPS on the handheld without much noticeable input lag.

I don't have any reason to believe this would translate into a good cloud gaming experience though, because it mostly seems to have become viable from local wifi just getting a lot better in recent years. I would expect the latency to still be pretty high for a remote server, and it's possible that the streaming server I use is just able to "correct" things more easily for a local connection in a way that a fully remote connection might not be able to.