"parts weighing as much as 100 kilograms could crash-land to Earth with scientists unable to predict where they will come down".
"The chance that anyone would be harmed by Tiangong-1's debris is considered highly unlikely."
“The chance that anyone would be harmed by Tiangong-1’s debris is considered highly unlikely.”
Unless of course you are hit by the debris...
Most of the Earth’s surface is unpopulated. The probability of impact is distributed evenly over the surface (implied by “unable to predict”). Therefore most of the probability of impact is distributed in unpopulated areas. The second statement you quoted is a corollary to the first.