Ionic will never post your app to be visible to be anyone you do not choose to share it with. The difference between “public” and “private” sharing has to do with the method you can use to share your project via the Ionic View app. By default, neither option is turned on, and your app is not shared at all.
When a channel is shared publicly, anyone who knows your app’s ID will be able to load it Ionic View. This means that you could, for example, post the app’s ID on your website, for the general public to view it.
When a channel is shared privately, only users you explicitly invite will be able to view your app. They will receive an invitation containing a unique share code, which expires as soon as it is used (or after 24 hours if unused). This user will then have access to your app via Ionic View until you choose to revoke it. Private sharing also allows users to submit feedback, which you can read from your Ionic Pro dashboard.
You can read more about sharing with Ionic View and watch a video walkthrough here.