ballpoint

Are you signed into your Google account on the TV? If so, have you checked the YouTube viewing history on your TV to see if those searched for items were actually viewed on your account? Also click on the "You" to check that it is your account that's linked to that YouTube version. We have three smart TVs at our place and I am signed into one of them, but the other two have no account set up. If I do a YouTube search on my phone or my computer (where I'm signed in), it will also show up on the TV I am signed into, but not the other two. If I do a YouTube search on one of the non-signed into TVs it will not show up on any of my other devices, despite all being connected to the same wifi network. Therefore I can't see how someone just using your wifi would show up on your YouTube search history, they'd have to be signed into your Google account on their device (or breaking into your home and watching YouTube on your TV). If either of those are the case, you have a problem. Change your Google password immediately.

Or if they were cowboys.