Why does the conductor call Valli 'madam'?

The conductor calls Valli 'madam' because of her confidence. When she was trying to board the bus, the conductor stretched his hand to help her, but Valli didn’t take his help and said that she can get on the bus by herself. She tried to behave like a mature lady. Therefore, the conductor tried to crack a light-hearted joke by addressing her as ‘madam’.