The majority of people address others based upon how they appear, and likely do it without consciously being aware; pronouns typically come naturally. Look like a guy, addressed as so. Look like a girl, addressed as so.
Despite what may seem obvious to you that should indicate what someone wants to be called via pronouns, with more and more people appearing androgynous, it's entirely too difficult to really know without actually being told.
However, yes - perhaps the person could have simply avoided the pronouns altogether, but when I used to work at a retail store, it was part of our directives to use sir and ma'am when speaking with a customer at all times unless the customer specifically requested otherwise.
Whether or not this person was deliberately using the pronouns is unknown; but until it is known, I see no reason to become upset. I hate being called sir, but I understand why others do it. I look like a guy, thus - common sense.
No one can read another person's mind; speak up or let it go.
