Its based on the theory of magnets. Magnets have two poles. The Earth has two poles. If the Earth is Flat, it has two poles. Makes sense to me.
No. It had nothing at all to do with magnets.
It was to do with the fact that Earth was a rotating roughly spherical object.
A rotating object has an axis of rotation. This axis passes through 2 points, one at the north and one at the south.
The location where it passes through the north side is the north pole, and the location where it passes through the south side is the south pole.
The decision of north and south is based upon the right hand rule (at least now) where if you wrap the fingers on your right hand around the object, such that it rotates from your palm to your fingertips, your thumb points north.
Meanwhile, for magnets it is only an ideal dipole and the like which has 2 poles.
You can combine the dipoles to make a single pole at the centre with a ring of opposite polarity, or you can have a multipole, where a common example is a common fridge magnet.
The men you discussed were not trying to filocate a south magnetic pole (note: A, not THE. Due to Earth's magnetic field not being an ideal dipole it is possible for Earth to generate multiple poles which likely occurs during polarity switching). That is quite accessible, being quite close to the Antarctic shore (and now in the ocean), and quite distant from the geographic south pole.
The pole these men set out to go to (again, they weren't trying to confirm its existence, they already knew it existed, they just wanted to go there) was the pole associated with rotation, where the stars would appear to remain at the same height and circle around you. It had nothing at all to do with magnets.
For a FE, it can have 2 poles associated with rotation, one on the top side, one on the bottom, and the same can apply as a magnet.
It could also be like a ring magnet, having one pole in the centre and a ring of opposite polarity.
Having 2 discrete poles just asks why this location is special. And that is one major problem with the bi-polar model. Why is any longitude preferred? How do you decide which is the magic one which has a straight line connecting north and south?