[altern8tif]

Wouldn't it be easy to test your hypothesis even further?

Instead of a random conversation, keep repeating a certain outrageous/uncommon phrase (say Korean cuttlefish snacks) and monitor your feed to see if any weird ads appear.

My guess is that Facebook/Instagram probably categorised your profile as someone who enjoys the outdoors and watches movies (which can be said of a large proportion of the world population), and knew that you might have been hiking then (location tracking and possibly via your face appearing in a friend's post?). Consequently, a "relevant" ad was pushed to you.