unexpected profile YouTube app
A boarder has been living in our house for 2 months. I have a Roku ultra connected to a home theater system with a projector and AV preamp. Two floors below, in the boarder's room, there is a non-smart TV with an Apple TV box. The boarder watches Youtube on the Apple TV using his personal Youtube login and he has been the only user of the YT app on the Apple TV.
I am the only user of the YouTube app on the Roku Ultra. A few days ago the boarder's YouTube profile showed up, along with my own on the YT app on the Roku and I can switch between his or my own without logging in to accounts. My YT profile does not show up on the Apple TV. The only common factor between the AppleTV and Roku is that they are on the same wireless network.
Am I misunderstanding something or does this situation seem like an obvious security problem with the Roku YT app?