Delta 9 THC is a naturally occurring cannabinoid found in abundant concentrations in cannabis plants.
While some variants of Delta 9 are created through a chemical conversion process that make them considered synthetic or semi-synthetic compounds, Delta 9 on its own is completely natural.
Hemp manufacturers are able to make use of the Delta 9 that naturally occurs in hemp because it's a byproduct of the CBD isolation process.
On the other hand, Delta 9 THCO acetate is not found naturally in cannabis plants and must be created artificially.