My first thought after reading the scene with Henry and Catherine was that Tilney is, indeed, a flirt! And what was also rather striking to me was that Henry had more feminine pretentions than we read Catherine having (knowing muslins, knowing journal writing), and yet we hear first of Catherine as a girl who has a tendency to have fun in masculine activities (at least until she was 14...) such as cricket, rolling down hills, and the like.

As for being totally smitten or just a flirt - I was thinking maybe Henry saw Catherine the previous evening, having no one to dance with, etc., and as he may not have known too many people in town himself (we don't really know that from the book at this point), he thought he would suggest that the master of ceremonies address him to her for the purpose of dancing (since they didn't speak much at first, and he must have felt she wasn't off-putting during dancing.) I don't think he was smitten by Catherine, but he liked what he saw of her well enough to be pleasing to her (but not enough to bother telling her he was not to be seen for the next few days, or where to meet up next.)