Hi Till. I had the exact same experience. I´m guessing that, as me, you never went to the Loot Cave (or went, but you hadn´t visited the spot ever since). With the new missiond and the infamous Urzok bounty, it´s easy to go int that spot one way or another. So as the others have said, it´s an Easter Egg reminding us of the Loot Cave days. It´s still creepy as hell, tho.