No, you haven't jumped over to an alternate timeline. The bombing was part of a civil defense awareness exercise. As part of the effort the Buffalo News printed a special post-apocalypse edition. Conjecturally, the bomb wiped out most of their staff and they were forced to use a still intact printing press in the suburbs. As far as I know this is the only prop newspaper ever officially sanctioned by the US government.
Ironically, much of the destruction described in the story would actually take place years later. All those factories and industrial facilities would indeed disappear, but it would be foreign competition and not a nuclear fireball that claimed them.
I stumbled across the Buffalo exercise while researching a similar effort held in Utica, NY, just down the road from where I live. It was the largest civil defense exercise in US history, using thousands of volunteers from a wide radius around the city to simulate a full blown nuclear attack and its aftermath.
The area in the newsreel where white suited teams are checking for radioactive contamination was, until recently, one of the most contaminated industrial sites in the entire nation. The soil was so saturated with coal gas waste that it would puddle up in your footprints if you walked across the grass.
