First thing i thought about was cannibals. They probably hitted some native population that kill whatever comes on there ground.
Also explains why they cut the tent, maybe they heard one of the guys that was outside scream because he was getting killed, or somebody jumped the tent at the front of those cannibals and they cut the side and run away. or maybe one person was infront of the tent and fell and another one was like fuck i am out and cuts it.
The more information gets forwards, like they find a tree with a sign on it and a tribe that does sacrificing, i would say yea that's the most logical solution.
The man in the snow confirms it even more.
Then them covering it up as "frozen to death" is to stop people from interfearing with those people. Destroying them and leaving them could also be a warning for the next person or they knew people would search for them so they kept them away from there camp.
Could also be one was a psycho murdered with a death wish and basically pulled them all in that forest to kill them off, or militairy that raped and murdered them and wanted it to look like something mysterious.