Likely it is, yes.
See, here's the thing that many people fail to remember--each species has its own requirements. Powdery mildew is a type of fungus (mold). It requires living plant tissue to live, survive and spread. So, anyone concerned about PM getting on or in their harvested buds isn't looking in the right direction--that would be a mold that lives on dead tissues in particular conditions (dry rot in a home, for example).
Other molds, like mycorrhizal fungi, require living plant tissues to live in symbiosis, that is to say they cannot live without each other. I think that's the most likely type of mold you're observing.
Finally, if the plant itself isn't showing any kind of disease symptoms, there's no reason to suspect it's sick at this point. And, even if it were, what mold would grow both on the soil and the plant?
