Japan had a lot more wood-only city buildings back then compared to the colder climate in Europe, where more massive stone architecture was common. In Europe, cellars are also common/default, unlike in Japan.

During high heat firestorms, most of the wooden material burns up and the ash gets carried away. The photo definitely shows cleanup and very likely was not taken the day after the bombing, but a single firestorm definitely can produce these results, much like other examples in Cologne, Hamburg, Dresden, Würzburg,... Except those had much more stone rubble standing afterwards.