The group left the cabin, doing exactly what they intended to do when going to the canyon, uncovering its truth.
A stronger desire is born within, a desire to uncover the truth about the fog and get their hands on all the treasures of the old dark elf.
They did not know it was a setup from Arthur, but why would they know? After stabbing him and throwing him inside that canyon to die, Arthur would not be merciful to those people.
He was already visualizing their faces of disappointment after finding out there was no such thing as treasures. Well, if they reach that far.
Arthur learned from their conversations that it was not the first time they had gone to that canyon. They had more information about the mysterious fog than most people.
Would this information lead to the truth? Arthur did not know, but he would try to help them in the background if things got too dangerous.