I'm not sure a YouTube initiated connect will trigger screen cast prompt dialogue. I can't easily test this as I would need to factory reset my Roku to confirm this properly.
Similar thing happened to me. Could it be that when one is casting their Youtube from their phone to their TV, the inadvertantly also cast it to the TV in the next room?
I have a related issue, but reversed. While watchingcYoutube on my Roku, literally in the middle of a video, I get a notification that I am now logged into (some random account I don't know) and I have no idea how or why this is happening.
YouTube on mobile phone snagging your TV over WiFi. Doesn't throw a prompt on the TV, not sure YouTube on roku has a setting to prevent this.
Complain to google.
I have a similar issue. I'll be using it at my apartment then mid video, YouTube will switch to another person's account. Someone I don't even know. This has happened with 3 different accounts. I just log out and switch back to my account, by why or how does this happen? I assume these are all accounts of people who live in my apartment building.
I think that they were using their phones to cast YouTube onto their TV, and inadvertently casted to your tv. You can disable the casting function on your TV, which means they won't be able to cast to your tv. But conversely, you will no longer be able to use your phone to cast to your TV. It's a trade off.
It happens to me fairly often. I use my Roku at a fire station and people often inadvertently connect the youtube on their phone to my roku. I just sign them out and it disappears and then log back in on my account. No harm is done, the offender is unaware that anything is different. To date, I have found no solution to prevent others from logging in.
OK so this just happened to me
Me and my roommate use the same internet and both have roku tvs
Somehow while I'm using YouTube YouTube we are in separate rooms I am logged into his account on my TV
I was actively using my TV no way he logged in with his phone or came in here and did it...I honestly believe that their programming is bad enough that my TV got his information on accident and boom bop made it where I'm logged in. Not cool youtube/roku.
I am not sure exactly how it is happening but I have been in a hotel for 3 days. Of course, I brought my Roku with me and connected to the hotel WIFI. On 3 different occasions in 2 days, there have been other accounts that have logged into the YouTube app on my Roku. Twice while my daughter was actively watching videos and she yelled for me to say someone else logged in.
The YouTube mobile app and YouTube channel on roku together behave in a way that tries to be helpful but is insecure where there are lots of people in close proximity.
If YT mobile app can "see" a casting device nearby (Roku, Chromecast, maybe others) then it will prompt to login the YouTube app on the device. Most people will just OK that prompt, not understanding what it is doing or assuming it will connect to TV just in front of them (which in this case it does not, but people will just go huh and not think further).
AFAIK, it is only YouTube app which does this. (Would be kind-of helpful if some other apps like BBC which need a login did something like this in a secure way).