Vitamin C is a chemical. There’s no way around it. Here’s the wikipedia article on Vitamin C, which lists the chemical formula and shows a picture of the structure. As a chemical, there is no difference between “natural” and “synthetic” vitamin C; they both have the chemical formula C6H8O6 . They might be talking about the beneficial effect of the chemicals that come along with the vitamin C found in the camu camu, but that has nothing to do with whether the vitamin C itself is natural or synthetic.
By the way, camu camu is actually second on the list of fruits with high vitamin C content. The kakadu plum is up to 5% vitamin C by weight.