My inlaws who live FAR away, and can not possibly be connected to my wifi, are casting to my TV. They are not associated, or permitted as members of my "home" in Google Home. Yesterday somehow, they are able to override our Cast from AmazonPrime, and start casting Netflix to our living room... from THEIR living room Google Mini. WTF??
Answered! Go to the Recommended Answer.
We haven't heard back from LukeM, and it's been a few days, so I'm locking the thread. As always, feel free to make a new thread if you have any more questions or concerns.
Thank you for your help, djtetei!