I respect his opinion, but I think he's completely wrong.
By hiding your relationship, you're essentially telling people you're doing something wrong. From there, fans feel justified to get mad at you for living your life and not dedicating every single second of it to them. It makes them entitled.
Fans need to learn that there are limits and that idols aren't their propriety and they don't get to decide how they live their lives. If they want to post about their relationship on instagram, they should be able to. If they want to go see a movie in broad daylight, they should be able to.