@RedlineAlchemist
More like the price for "wasting food".
Funny enough, even though their food is terrible, I believe it means that if someone makes something so filthy it is inedible and hence "wastes food", the penalty is death.
If they live in a desert and food is one of their most valuable resources, it would mean their race has gone several times through extended periods of hunger with barely if any food, so it would make sense for them to have a severe punishment for someone who wastes food.
Decapitation is somewhat too severe a punishment, but if we consider it might have been a rule created during those extended periods of hunger and someone wasted food and made others go hungry for even longer, it would make sense why they punished that person with death and made it into a rule which their culture keeps even at times where food is more available.