Readers are not specifically told what has happened to any of the homes in the neighborhood. We are told that the house in the story "stood alone." The rest of the city is complete rubble, and only one house remains standing.
The house stood alone in a city of rubble and ashes. This was the one house left standing.
Readers are given a hint that the area has been destroyed by some kind of nuclear disaster. We are told that the city gives off a "radioactive glow" that can be seen for miles at night. What we don't know is the cause of the hinted at nuclear disaster. It is likely one of two possibilities. First, it could have been a nuclear bomb similar to the bombs dropped on Japan to end World War II. Second, it could have been a nuclear reactor that melted down and exploded similar to Chernobyl. While that particular disaster had terrible radioactive fallout, it didn't have the same kind of explosive destructive power as a bomb. With that said, this is a fictional story and writing about a nuclear power plant blowing up an entire city is not a unique idea.
Regardless of what caused the explosion, a nuclear explosion that incinerated everything within the blast radius is the likely reason that all of the city has been reduced to rubble. Why a single house was left standing is unknown, but it isn't completely fiction. Random buildings/houses were left in tact in Hiroshima and Nagasaki. Additionally, Bradbury's information about the shadows left on the wall is based on historical evidence as well.
The entire west face of the house was black, save for five places. Here the silhouette in paint of a man mowing a lawn. Here, as in a photograph, a woman bent to pick flowers. Still farther over, their images burned on wood in one titanic instant, a small boy, hands flung into the air; higher up, the image of a thrown ball, and opposite him a girl, hands raised to catch a ball which never came down.