The horse is merely hoping to get nice, but has to be taught that humans don't have to be groomed. Although horses don't do this all of the moment, they have a tendency to do it when particularly relaxed
so nurturing. look how excited they are about the baby. all of the females welcome the baby into the herd. so human. I once saw a nature program on TV where they filmed wild horses welcoming the new baby into the herd, just like in this photo.