They were already looking not at the tent, but at the luminous unknown Power. Looking at the tent and seeing it wouldn't do them anything. They couldn't see it anyway. They were staring at the luminous Power that they thought was still in the tent. They didn't see it there. The unknown coercive force was probably watching them from the forest.. The other trio, unable to see the unknown coercive force in the tent, decided to return to the tent. This means that there was a trio in the cedar tree. The trio(Dytlov, Zina,Rustem), the boldest, decided to return to the tent. The other cowardly quartet decided to dig up and go into hiding. So the reason they digged the lair was to hide rather than protect from the cold. But there was no way they could escape from the unknown coercive force.