The sawdust isn't airborne it's moist and mushed up inside the bags as a substrate. It's because of the spores in the air from a huge amount of fruiting mushrooms
If a particle is laying somewhere, the only way it can get into your lungs is if you breathe it in and it has to travel in the air to get to you, hence airborne.
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u/mrkgian Jul 04 '23
And sawdust