• On your tv, go to settings > general > google cast > allow others to control your cast media : choose "never"
• install the google home app on your phone, click on the tv device, click the settings gear icon, "let othres control your cast media": never

This thread may help

I know these are talking about "casting" and you are initiating youtube directly from your tv device but if I remember correctly these options may still affect the behavior you're seeing

I think the device you're playing on pushes some notification out to any devices on the same network.

A little while ago I was playing music from YouTube music on my Google home speaker....and it starts skipping tracks for no reason and so I think something is broken... Turns out my GF didn't like what I was playing and was controlling it from her phone... She was on the same WiFi... We do not share a google accountn

You're connected on the same WiFi as your TV. And you're using same account in YouTube as on phone. It's normal, see it as a extra remote control.

Long Press on the notification, notifications, cast, disable

If it really bothers you, yeah just disable the notification.

To tell my ma I'm insomniac

Because you are probably signed in with the same account and on the same wifi network. It will allow you to control the tv app from your phone.

The title says it, google play services, that's it. Unable it and you're ready