a chromecast is basically a Google Chrome browser on a stick, when you're casting something, you send a url to the content to the chromecast and it loads that in its browser.
when you want to cast something without using data, the app pretty much has to be specially designed to do so. While I'm not entirely sure, as far as I know most apps don't (netflix / YouTube). I think the app called localcast does it, but I'm not sure.
yes?