Beneath the brittle rubble was still brittle rubble Dagon had sampled from five places, and all he found was this. In other words, the entire stone tower was indeed completely burned, not changed by a spell, or a fire mage cast some kind of fire that burned from the inside out. Only when stone is used as fuel can it be destroyed so thoroughly. It was like a corpse, being sucked and burned horribly were completely different, and this stone tower could be said to have been completely cremated.