It's hard to tell which is which and it's probably a bit of both. I don't really understand why whenever the living nature is being explained, it's done in a wa

It's hard to tell which is which and it's probably a bit of both. I don't really understand why whenever the living nature is being explained, it's done in a way that attributes to some design what really belongs to an accident of evolution. Species develop traits continuously and in a chaos, every individual is a mutant, then environmental pressure determines combinations that are most suited to reoccur (through reproduction). In this case two species found each other. Maybe a few springtails had the genes to detect the smell. Of those, a few found it pleasant, it could be that others didn't. Maybe a few streptomyces had the genes to produce the smell. A happy accident that allowed both these genetic traits to endure environmental pressure.