Well, etiquette is all about manners and if you feel that this man is only fishing for gifts, then that's ill-mannered and I see no need for you to feel obligated to send a gift on such a slight acquaintance. If I were in your shoes, I would wait to see if the promised invitation arrived. If it did, I would send a polite note stating my inability to accept, along with a card of congratulations, and leave it at that.
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Don't say "I can't" ... say " I haven't learned how, yet." (Reg Bolton)