There are two trains of thought on this.
Mono-Pole ModelProponents of the classic Mono-Pole Model argue that less than 1/10th of the human population even lives in the Southern Hemisphere, and the assertion that half the world is in error or mistaken is inaccurate.
Some people have claimed to have circumnavigated Antarctica. But did they really circumnavigate Antarctica, or could that be a mistake? Did they sail the requisite distance they were supposed to, assuming that the earth was a globe, and then head back up northwards to warmer climates?
Bi-Polar ModelProponents of the Bi-Polar Model argue that there are actually two poles and that the magnetic field lines resemble something like that a bar magnet, the compass pointing to either pole to take the navigator around it. The Antarctic circumnavigation is relatively unquestioned under this model.