a sad and tragic story.
Any lit flame produces carbon monoxide which is odourless and heavier than air so you can slowly sufforcate it will happen even in a tent or van even a closed room any lit appliance is dangerous if used incorrectly , sad times to all involved ,escaping gas can usually be smelled and too much in an enclosed space will ultimately go bang ,gas is a good slave but a bad enemy beware!
Agree, This will only be as a result of one thing, running a gas fridge within the confines of an enclosure/tent resulting in carbon monoxide poisoning which ultimately will lead to a slow but painless death.
Could it have been CO poisoning if the fridge was running on gas inside the tent? No smell and slow acting