Dried product varies pretty widely in strength, even from stem to cap. Things like strain and spore lineage also contribute to strength of the dried product.
They are using synthetic psilocybin. It would be impossible to make a translation between grams of dried vs. synthetic. Different species have diff content, liberty cap vs. penis envy etc. also stalks vs. caps typically differ in str.
Dosage guides for dried shrooms are already universal in recommendation of dosage typically speaking in terms of grams without bringing up the individual strain. This leads me to believe that a generally close conversion should be reasonable from the dried natural to that MG number.
There's no surefire way to estimate the actual weight of psilocybin save for extracting it chemically. It can vary widely between species, between flushes, and even between individual fruits.
A good place to find more info is here: https://www.shroomery.org/