Humidity plays a role in bud rot, for sure. But the real cause of bud rot is a certain type of mold making it into the plant from an open wound that is on the plant. Bud rot does not always affect the buds, either. It can affect stems, stalks, and leaves as well.
The name of the mold is botrytis cinerea, if you want to look it up and do some research.
I hope this helps. Bud rot is a scary thought.