Here's a theory: after your conversation with your friends, one of your friends checked out the Campari product on the web, and from there FB deduced that you might also be interested.
or facebook knew you were at a restaurant that served it searches for "Campari" are 1000x normal in this geographic area
I don't think even facebook can necessarily reveal "the reason" an ad is shown because there are probably several reasons (combined) which lead to each story and ad in your feed.