From what I read, ball lightening is usually accompanied by a rainstorm and thunder, lightening. Not sure if that was going on at DP, and I don't see them leaving the tent because of it.
Whatever it was made them immediately and without forethought, leave the safest place they were to get AWAY from it, or they were ordered out immediately by military that they feared.
They could have left the tent thinking if they started a fire, it might scare away the creature, bear or whatever, and the two climbed the tree as they saw it coming back.
The Rav 4 had to have their injuries inflicted at the place of death because they were so debilitating, they would not have been able to crawl there. Why did they leave the den and run toward the ravine?
There are so more questions than answers.