Viscose is synonymous with rayon, and the name comes from the honey-like texture that occurs during the manufacturing process. The main ingredient in viscose is wood pulp, making it hard to classify as either synthetic or natural. Though the wood pulp makes it natural, the manufacturing process (a very polluting one) is very much driven by man.
Any material is created through chemical treatment and then cooled, heated, or converted through additional chemicals. It would not be considered a “natural fiber”. So no matter what the product label says, rayon is still a synthetic fiber.