I assume that their feeling is based upon the addition of synthetics, not on any real understanding of the chemistry of what's been added. There has been a lot of looking into this and there's no indication of any cannabinoids bearing similarity to those contained in cannabis (ie: no tetrahydrocannabinols), though I'm not aware of anyone who's looked for and not found JWH-O81-style alkaloids.
Only the tetrahydrocannabinols and their analogues are covered under US and (AFAIK) international law. The pyridine and indolic cannabinoids like JWH-018/81 are entirely legal, and considering the relative ease (and the familiarity most of these places have with indole chemistry from tryptamine syntheses) of synthesis, they seem most likely.