In days gone by, when a reporter wrote a story, it was common to examine older material to get a background on the report or on previous reports that may have dealt with the same or similar subject material. On a newspaper, the reporter would examine older editions, the paper’s “morgue.” These days most of the material has been digitized for fast research.
Sure you just use Google or your chosen search engine to bone up on some background material, except that Internet research doesn’t discriminate against real or fanciful stories. But if you check a presumably reliable source, you can find a wealth of material. That assumes the publication in question doesn’t charge you a special fee to research older stories.
But some commentators don’t bother with the research. They just make things up. Once someone else picks up the original false story, the rumors can spread quickly.