This is earned for finding optional collectible #1. If missed on the first run, you can "Play Episodes" and select specific parts of the Episode in order to find the missing optional photos through
collectibles mode. The following collectible is described and can be seen in the video below at 1:00:
Found at the campsite, by petting the dog 3 total times. Between each interaction, they will move locations. At the end, they will dig up a collectible, and you can pick it up.
Getting all 6 collectibles in this episode will also reward you with the following:
https://www.trueachievements.com/a260746/lost-boys-chronicle...