Things like this happen. The police get whack job phone calls on a regular basis. It’s like those adds you see all the time predicting market calamities. After 20 years, they finally get it right by accident.
Many people thought Dallas was a bad idea for Kennedy. Speculation was elevated.
I'm sure that cops or newspapers occasionally get calls from some schizophrenic predicting an earthquake and,*voila!* an hour later there's a quake.