To sum up observations by several previous posters, there seem to be two factors at work here.
First is the way it is about inevitable that weird rumors will be generated whenever there is a sudden, unexpected distaster.
After the great San Francisco earthquake of 1906, it is said, it was widely believed there that New York City had been engulfed in a tidal wave. It was also widely rumored that animals had broken free in the zoo and were attacking people on the streets.
There was a historic tornado in St. Louis in the late 1920s. After the tornado passed through midtown and all was calm, my aunt was standing out on the street near her high school waiting to take a streetcar home. She ran into her father, who was himself a streetcar employee. He was carrying a shovel. He had taken off from work to help dig her out; Rosati-Kain High School had been untouched, but it was rumored all around town that it was just a pile of rubble.
The second factor is the faith the public puts in the news media, even as the mania to be first with the news impairs the ability of reporters to report accurately.
I didn’t remember the story about the State Department bomb. I do recall, though, there was a story about an airliner in Canada having been forced to the ground which was believed to be in the control of hijackers. I heard that once, and never again. That afternoon I tried going to the public library in Clayton, Missouri, the seat of St. Louis County. It was closed and the staff were all gathered across the street. Someone thought a bag of some kind looked suspicious, and the bomb squad had been called. I expect a considerable list could be compiled of similar panic reactions around the country that day.
While we would like to think that reporters, as supposedly trained observors, would be less susceptable to rumors and panic, it often seems that the reverse is true.
On the day Reagan was shot I was working a job where I was taking short trips in my car continually. For a while, each time I turned on the radio I heard reporters retracting or contradicting information from the last report I had heard. It was said that Reagan had been shot at but not hit. It was said that his attacker was in his 40s and spoke with a foreign accent. It was said that there had been a second gunman, and that he had been able to run away. At the time he was carrying a mysterious black box. I remember that last detail particularly because even when I heard it the story sounded like some garbled, confused rumor.
In a similar vein, in William Manchester’s book The Death of a President it is reported that shortly after President Kennedy was shot in Dallas a theater manager in Las Vegas announced to patrons that President Kennedy had been killed, and Mrs. Kennedy and Governor Connally and a Secret Service agent. The theater then proceeded with its scheduled movie.