Its just pure misunderstanding from there side. They look merely from a chemical an clinical point of view. Its creating a differnt state of reality so dangerous for the mind and can cause psychiatric disorders and erretic behaviour that can get people in dangerous situation (clinical). And Psilocybin is of the chemical family of the indoles , wich include also DMT and Serotonin wich clearly indicate it has effects on the brain chemistry.
I think that the clasifications in the Netherlands are much better done and cover the whole varity of aspects of a drug. I read a few including the one for "magic mushrooms" (so not psilocybin) and they look at many differnent aspects in clasifing these drugs like , harmfullness to the body, harmfulness to the mind, the amount wherein its addictive , the social setting (does it cause problems in the sociaty, look at alcohol !) is the drug attractive for orginized crime, how is the distrubution done and is there information avaialbe ect.
That will give you an overal view of how dangerous a drug really is , for 'magic mushrooms' the threat was not so great according to this evaluation.
Don't know how they do it in other countries but they must have a very different system to end up with class A !!!!