It makes sense that if one of the theorized physical phenomenon happened (slab slip, avalanche, rock slide, wolverine, etc.) that the hikers, after walking a certain distance, would stop and consider if the danger had passed. Why walk a mile to the forest being so poorly dressed? Why not take a moment to ascertain that whatever it was that made them flee was no longer a threat?
I can think of three reasons to head all the way to the forest:
1. Whatever happened affected a large area and the forest was the only refuge. Toxic missile fuel, for example. Their hope was that the trees would provide safety.
2. They were forced to leave the tent by outsiders and had no choice.
3. They were irrational and unable to think clearly. The poisoning scenario works here or infrasound.
Please add reasons that I have overlooked.