In Hiroshima by John Hersey why did Mr. Tanimoto look amazed when he looked over the city after the bomb

Mr. Tanimoto was amazed by the extent of the destruction. He initially believed that the area he was in had taken the brunt of the explosion, that the areas surrounding him would have suffered little damage. When he climbed onto the pile of timbers he was amazed and horrified by the obliteration before him.