5 grams is considered a heroic dose (e.g. the dose where you are likely to experience things like ego death).

Around 2 grams is considered a "museum dose" or "social dose" (e.g. it's enough to change your perceptions but not so much that you are unable to operate).

So 25 mg is a fairly low dose while 1 mg is very low.

5 grams of mushrooms is not the same as 5 grams of psilocybin. When taking about mg, I think they mean psilocybin. When talking about grams, it's mushrooms

I looked at the study and it appears that it's 25 mg of synthetic psilocybin. So assuming that's equivalent to 100% psilocybin and mushrooms average around .6% dry then it would be like 4g dry mushrooms.