" Again; the damaging object is CREATED by magic and PROPELLED by magic, but is not in and of itself magic. A spell that conjures a flight of arrows that deals piercing damage should be reduced by DR/bludgeoning or slashing. If it doesn't, then that spell's damage type shouldn't be listed as piercing at all"
seems like if it's listing a damage type then the creator is assuming that the damage is coming from the object, not the magic that created, moved, propelled it,thus it is not magic damage, it is damage from an object which has been altered by magic. They answered this a few posts back.