Not always. HHC is natural, but it is scarce, unlike Delta-8 and Delta-10. It happens when D9 undergoes oxidization over time and turns into CBN.
Since low THC levels are difficult to extract naturally. So, manufacturers hydrogenize the THC molecules and bind D9 THC from hemp with hydrogen atoms. While hydrogenizing D9 THC makes the HHC molecules less stable, adding hydrogen makes them power powerful than D9, becoming semi-synthetic.