People just get things wrong. They read them wrong, or remember them wrong or the way they want to, or the information they read right was wrong in the first place. You hear the same a fact a thousand times, but if you track down its origins, you find out all the repeaters are using the same source, and source zero was just guessing, or citing a highly questionable source or study. Or misciting a highly questionable source or study. Or confusing the details, so that by now, everybody’s under the erroneous impression that a shot of espresso contains more caffeine than a cup of coffee.