Hey there Randy9979,
I apologize about the late response, thank you for being patient! Were you able to find the answer to your question? If not, I'd be happy to help out! So, the only way someone can see what you are casting is if they are also connected to the same Wi-Fi network. There is also a way to prevent others on your Wi-Fi network from controlling your casting, that is by disabling cast media control notifications.
I hope that answers your question! If you have any other questions or concerns for me, please let me know.
It looks like we haven't heard back from the OP so I'm going to go ahead and lock the thread. If you have any further questions or concerns, feel free to create a new thread.
Have a great day!