Repentance has a public aspect and a private aspect. Jesus speaks very clearly about doing one’s repentance in secret -- not chattering on in public about how hungry your pious fasting has left you. At the same time, the church also has a ministry to call -- publicly -- for repentance, to sometimes play the role of John the Baptist. Calls for repentance happen every week, every day, inside religious buildings, inside religious communities. Sometimes calls for repentance need to happen out on the street corners, too.
Still, this is a strange thing to do, this liturgy outside a hospital. It does not feel entirely comfortable to me -- but I am not sure anything about Ash Wednesday ever feels entirely comfortable.