I believe it’s .4 calories per serving which is less than one and which rounds down to zero, but it’s not approximately zero by a long shot.

How is 0.4 kcal "not approximately zero by a long shot"?

Especially when compared to a standard coke with around 150 kcal.

Well, it’s almost half a calorie, to begin with.

By the time I finish the can I'll have Burned through more than 0.4 calories.