Do you notice other things that he’s forgetful about? I would find it concerning. Is it possible he slept through parts of it when you were watching, and that’s why he doesn’t remember? Recently I was talking to a friend about the movie “Nomadland” and I mentioned a scene that she didn’t remember. She said when she watched it, she fell asleep toward the end. She went back and watched the end again, and saw the scene I was talking about.