The paper stated James Fadiman as the source for the characterization of a microdose, it however failed to properly convey his point of view.

I've heard James Fadiman reporting twice that it is 10% of a recreational (1-3g) or therapeutic dose (3.0-3.5g), but certainly not 10% of a heroic dose. This study went with 0.5g which is 10% of what's considered a heroic dose.

The effective dose is considered to be 6mg if psilocybin or 0.6g of dried magic mushroom, thus the amount given in the study is very close to being detectable (and incidently was in most of the cases) which I don't think you can charaterize as a microdose. James Fadiman expressly stated a microdose would be a dose that you couldn't detect and would forget you had taken while going on about your day.

If one is taking 0.2-0.3g of dried magic mushroom this would be, without question, not getting high.