Oh Sokka? Sokka's a dreamboat! And that's probably something his little sister doesn't want to hear.

"Sister Nima, of the Eastern Air Temple." Nima bows with cheerful, polite formality. "I've met your brother. He's a good man. He has a lot of integrity."

And Katara's name and family rings a bell in Nima's mind. Aang hasn't spent a LOT of time talking about her - there seems to be some sadness wrapped up in mentioning her name and their relationship - but it's been clear that he is deeply attached to her, in a way that is not cohesive with the Air Nomad philosophy, but which may be necessary to the philosophy of being the Avatar.

"You're Brother Aang's girlfriend, aren't you?"

Which is a strange thing to say of any air nomad, but Aang is a special case.