I believe you are referring to the webview.
In my experience, the person whom the camera was shared to was prompted to add “Cam Plus” to my shared camera when they attempted to use the webview - which was ridiculous since I had already subscribed to that for the camera.
My examples posted earlier were using the mobile app - by “navigating away” I was implying moving their view from one camera to another - on the chance they had more than one to observe.
In my experience - as long as the 3rd party kept their mobile app focused on the previously shared camera - there is no way to prevent them from continuing to view it - unless THEY break the connection by switching to a different camera.
Power cycling the camera itself did noting to prevent viewing the camera when it came back up.
Lesson learned - be be wary of whom you share a camera with - assume you are sharing it forever.