Untrue. Yeah, KFC markets chicken as a Christmas tradition, but every chain shop, convenience store, supermarket, shopping mall, car dealership, sports shop...anything and everywhere rides the bandwagon for marketing holidays. This is just one of the better known ones. No one I know has ever made a Christmas feast of take-out KFC. It’s just a thing that’s been in popular culture for 50 years or so, so it gets international attention. Some people like to get a bucket of chicken on Christmas for their families simply because it’s funny and something they probably remember growing up with as a child. There’s no actual “there, there” in the way foreign media always repeats this story every Christmas.
I never took it to be a widespread thing. Just enough of a thing where pre-orders make sense. Sounds like a fun, silly tradition for those that do it.