He is referring to the announcement by Google at Google IO that mentioned being able to stream via proximity without having to be connected to the Local WiFi.
The CCast itself still needs to be connected to a WiFi AP but the phone that is sending to it does not.
It will use location data and show a code on the screen to make a connection over Cell Data.
What they didn't mention is what can be sent to the CCast...
Is it locally stored content?
Is it merely a way to get control and connect to the CCast (For gaming use)
Or does it allow you to do everything you could do if you were connected to the local AP without having to be connected to the local AP...
One thing that is certain is the CCast itself STILL requires having an internet connection and Wireless AP to connect to.
Which the link you posted will help if no other AP is available.
Unfortunately while they announced that feature I don't think it has been implemented or made live yet.