This is partly because writers are ingenious people, who come up with all sorts of ideas, likely and unlikely, and partly because if you throw out enough predictions some are bound to come true eventually.
And then there's the even more frequent cases we tend to overlook, where authors made predictions which turn out to be totally, unequivocally untrue.
I spotted something of the sort when reading some Agatha Christie stories recently, in her early book POIROT INVESTIGATES (written 1923-25, collected 1925). In one story set during The Great War, she has a plot-line involving an assassination attempt directed at the Prime Minister, immediately followed by a kidnapping plot. Her two main characters, Poirot and Captain Hastings, discuss the assassination attempt thusly:
HASTINGS: "I was asking you what you thought of this attempt to assassinate MacAdams"**
POIROT: "Enfantillage!" replied Poirot promptly. One can hardly take it seriously. To fire with the rifle -- never does it succeed. It is a device of the past."
HASTINGS: "It was very near succeeding this time," I reminded him.
Poirot shook his head impatiently . . .
And just about forty years later, the most famous political assassination of the twentieth century took place, with a rifle.
So, no cigar.
*not as hard as you'd think, given that it was well known that the modern superliners of the time carried far fewer lifeboats than there were people on board (typically enough for half the passengers and crew, or less). H. Rider Haggard even wrote a book about it as far back as 1888, nearly a quarter-century before the Titanic disaster.
**Christie gives her fictitious wartime Prime Minister the name David MacAdam, nicknamed "Fighting Mac" for his ferocious (and, to Christie, wholly admirable) opposition to Pacifist attempts to end the war in a negotiated peace; Christie assumes throughout that any pacifist movement must be funded and controlled by German agents and might lead to "a premature and disastrous peace" (!)