There might also be the possibility that the keys were left in the car, thus preventing the steering wheel lock from holding the steering position. In that case, depending upon which wheel first contacted the beach, the steering could have suddenly changed direction. That is, it went over the edge whilst steered to the right then, on contact with the beach, steering span back to the left.
Leaving the keys in the car may not be that unlikely. Personally I find a hire car’s keys a bit of a nuisance to carry, as they are not attached to my other keys. The hirer might have assessed that since there was obviously no realistic possibility of theft in such an idyllic spot, leaving the keys in the car would do no harm.