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.
And here's another theory: you were already targeted by the Campari ad before, but you were not consciously aware of it. This triggered the conversation with your friends.
That's amusing, but at the same time it could make an excellent business idea - restaurants could tailor their menu based on the preferences of people who're booked to eat there. If you knew that a group of people who all really like sea bass are arriving at 6pm a restaurant could put a high-profit sea bass special on the menu knowing that those people are likely to order it. The customers are happier because they get their preferred dishes and the restaurant is happy because it makes them more money.
No, rather Campari started a multi-channel(?) campaign that included Facebook ads as one channel, and (various) 'real-life' channels to prime OP to talk about Campari 'randomly'. Could be anything from hired 'stooges' to tv ads to billboards to a new item on a menu.
Or, one of your friends had previously been targeted for Campari ads; FB knew you were with your friend, and now serves you some ads it knows would be appropriate for your friend.
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.