It's called supersampling, my friend. See that here. You can have a native 4K resolution monitor but increase the internal resolution of the game to make things even sharper, granted you have the overhead to support it. Hell, if you can do it, you can render a game's internal resolution to 5K and beyond on your native 4K monitor.

But that's not what's happening in Stadia right now. Right now, until the developers optimize their game and learn the platform, what we're experiencing is internal game resolution upscaling on the stream side of things. Again, Google isn't making false claims about anything. I had to break it down to make that clear. Stadia is working as intended, even in these early days.