@Lynn118 Happens with regularity to tons of hosts. Many threads on this forum about it.
No, I don't think there is any point in asking the guest about it. Airbnb tells guests that a 4* rating is "Good", so that's what guests think they are doing- giving you a good rating. They aren't marking you "down" or trying to hurt your ratings, or insinuating that there was anything wrong with their stay. Most guests have no idea that Airbnb holds hosts to such absurdly high standards that a 4* isn't good for hosts.