[Deep link is] When a clicked link or programmatic request invokes a web URI intent, the Android system tries each of the following actions, in sequential order, until the request succeeds:
- Open the user’s preferred app that can handle the URI, if one is designated.
- Open the only available app that can handle the URI.
- Allow the user to select an app from a dialog.
Source
iOS and Windows have their own versions of this but point being that if you click some link opens up and client with confirmation dialog to join a network.