"natural flavor" is a BS term they use for synthetic flavor additives.
They take "natural" ingredients, break them down into individual compounds, and then put those compounds back together into a "flavor".
It's like how Coca Cola makes "Simply" Orange. They break down orange juice into discrete molecules and elements. Then they recombine them. But because they started with "Orange Juice", that's all they put on the label.
It could be literally anything.