"Android TV" is literally any smart TV that runs Android with Google's blessing. Analogous with "Android phone".
Chromecast with Google TV is more in line with Apple TV, FireTV, and the now discontinued Nexus TV.
Chromecast with Google TV is more in line with Apple TV, FireTV, and the now discontinued Nexus TV.
How is this different?
Usually, the actual TVs that run Android are marketed as "Android TVs". It looks like streaming devices like Nvidia Sheild do so too when they're in fact not "Android TVs".