I honestly have zero romantic attraction to her anymore.
Your emotional response does not square with this statement. If you truly do not care, then I don’t understand your reaction.
Not having romantic attraction for someone and not caring for them are two different things. So his concern for her well-being definitely makes sense to me.
I too would worry about my parents, my brother, my closest friends if I lived with them and knew they were out at a bar...and I was home waiting to hear if that door closed so I knew they got home safely. I think there is at the very least some type of bond that happens with many people with they co-habitate that would elicit worry in a situation like that.