I had something similar happen recently. I purchased a new Roku sound bar, and after I set it up, I noticed three different apps were already logged in as someone else.
The first two seem to be the same person's login\name, so I assumed I had been re-sold a soundbar that had been returned by someone else who'd set up some apps. But, the third app had my sister's login ... So, I ruled out the bought-a-returned-product theory
I have an apartment in my basement that uses a Wi-Fi extender attached to the main / upstairs house. My best guess is that somehow the internet connection is remembering what people did on the Roku downstairs.
The downstairs has its own Roku set up (just a regular Roku, not a sound bar). The two Rokus are not at all connected to each other intentionally, and there is no way someone could have logged on to the new Roku sound bar in the few days since I bought it.
It's still a bit of a mystery, but this is the only thing I can think of that what explained the new Roku sound bar thinking that three apps had already been logged into.