Not dietal calories.
The calorie numbers we assign to food, measure how much energy our body extracts from them when eaten.
In this context, plutonium is closer to 0
If we instead want to measure the actual total physical energy content of materia, we would turn to E=mc^2, telling us that a gram of anything has about 20 million kcal, no matter if its plutonium or diet coke. which is a slightly less useful value on food labels :D
they wrote ass backwards ass backwards. It’s a joke, not self censorship.