Please notice that the cloud icon also downloads the page/book HTML, and all the other resources you might have in it. It's not just the video
If you want to do that in the official Moodle Mobile app, I don't think you'll be able to hide the cloud icon using a remote theme since CSS is not aware of the files in each page.
But looking at the other post I guess you're building a custom app.
Unfortunately our core team do not have the resources here to help people use the open source code version to build custom apps. We provide a service where we can customise the app for anyone who needs it including the Push notifications (Airnotifier) service management. This service helps fund the improvement of the app in general: https://moodle.com/mobileapp/
As a tip, resources have a list of the files they include in module.contents. You should implement the isDownloadable function in the prefetch handler of the module affected (page, book, ...). In case of page, $mmaModPagePrefetchHandler.Cheers,
Dani