My husband also went through a phase where he believed that he had seen everything on tv, even when it had never been aired before.
Maybe it was because the plots of many films or dramas followed a similar theme and it triggered memories of things he had indeed watched, as for news items history repeats itself quite often, just in different settings, so again I just accepted that it was triggering memories of other events somewhere on the world stage.
As for wanting to watch something myself, I found that my husband was more than happy to sit through something he'd already seen if I said something along the lines of "I know you've already seen this but I must have missed it, would you mind if I watch it now?"
Fortunately, he was generally very considerate towards me and more than happy to sit through something again if it made me happy.
TV viewing became more of an issue for different reasons further along in the disease and eventually we could only safely watch things which had been seen, tried and tested in the past. If I wanted to watch something with an unknown content I had to find ways of doing so alone - but for the 'deja vu' stage I found that acknowledging his disappointment and asking nicely definitely worked!