He was definitely fighting gravity. You can see it at the 20 seconds mark. I am familiar with that sand on the sides, that means turn the steering wheel and go down the dune.
It seems that when the passenger distracted the driver they ran out of dune to fight gravity with on the left side and the car just flipped on the right side where there was still sand so two big mistakes right there.
I agree Jeeps are a bit unstable specially two doors I've driven the 4 doors of some friends and tend to be more stable than 2 doors. But 2 doors are more fun because of it. You have to be quick to correct the steering or else this happens.