Well, it sounds like it's a mystery for the ages then, now. It could have been some sort of rot- which is just a general name for a fungal takeover of some sort, and there is more than one sort.
I had a new one recently. Less than two weeks ago actually. After battling rot on a Pineapple Chunk for most of it's flowering, I harvested it, and its neighbor- also a PC but without mold issues. Then I loaded my drying box up with the two plants worth of bud, and (for some reason) tried to do a very long initial drying session- by closing off most of the vent holes for the box. It seemed to go well the first week- then the next week I returned to find a light gray mold, with long silky hairs, was starting to cover the surfaces of all that bud. It was just on the surface- and not the same as budrot - more like something you'd see growing in your refrigerator, if your refrigerator was like mine would be if had a refrigerator, which I don't, because I live in a natural big refrigerator.
Anyway- that little skiff of mold covering everything seemed so thin and harmless somehow- like I should be able to just blow it or wipe it away- but I had to admit that the bud was ruined. On the bright side I got over two ounces of hash out of it, along with some other trimmings.