"Of course. I would hate to leave them out and risk insulting your great cultural heritage."
Either she had no idea who he was, though in all honesty how many people in the galaxy hadn't heard of Leto Atreides II? The pilots themselves needed spice to navigate the ship so precisely through space. Or, Oswin was very boldly continuing to treat him as casually as she did for as long as he allowed it.
She was either very brave or truly didn't understand the power he was capable of.