Confusion of French Etiquette

Maybe someone can help me out here.. In chapter 3 when Jake Barnes meets Georgette Hobin, did they know each other previously? Because she just plops down at his table and the two carry about a normal conversation without much introduction. I'm not clear if this is just how they kick it in France or if they have a certain history together that the author has yet to reveal. Another thing that confuses me is the next scene when they meet with Jake's friends (ie Mr. and Mrs. Braddocks, Robert Cohn, Frances). On page 25, Jake introduces his "new" lady friend Georgette as his fiance? They just met! ... I think? I've come to two conclusions: this is French etiquette that is foreign to us Americans, or it is simply a joke. Can anyone clear this up for me?