It is not possible for a roku to spasm and suddenly know someone’s authentication credentials and log into their account. I work in security. I literally research security vulnerabilities all day long and I have never heard of such a thing. She or he had to have entered her credentials into the device. There is no bug or automation that could brute force a password and pic a random account that just happens to be someone you know.

The fact that he lied off the jump speaks volumes. He could have just said “she let me borrow it”. That is way more believable.

Trust your intuition here. I’ve been in a similar situation to what you describe. It’s the reason I got into security in the first place.