Who or what killed the camp of people in so little time?

Question

In the Walking Dead S4E07, Phillip (who now goes by Brian) Is on a supply hunt with the camp people that got him and Brian's step daughter out of the walker pit.

The 3-4 men come across another camp with about ten surrounded by wire, and consider looting them and robbing them of their supplies. But the apparent leader said they go find their own supplies.

They are on the same hunt, same day and time when they circle back and are surprised to see the people at the camp dead.

They weren't killed by walkers because the walkers would have had a nice meal out of them and stayed.

Who killed the camp people?

Answer 1

Killed by forest grue, for staying too long on same location.

On serious note, it is a bit Deus ex machina moment, because it serves perfectly for Phillip/Brian to switch back to old habits.

It is unlikely that Phillip/Brian did it himself because he was not parting with the group, although it is totally the way he would handle it. It is also unlikely that hunting group didn't hear any gunshot as they couldn't go that far and back. So unless there is super efficient group that uses silencers and can attack without any defender managing to fire back, it is too obvious Deus ex machina moment.