Well for one, the way it is depicted, is circular. Secondly, it shows that all continents convirge in the middle, which is the north of thd glibe, the are much further spread out below, same with the globe. China is in the northern hemisphere, they have a detailed map of the continents above a certain lattitude.

But, Antartica is in almost unattainable waters without sufficient supplies and technology. It is very cold, even for modern technology and thermal wear. Icecaps are more present, and sailing that far south, well you see not much of anything for much further. To discover australia, there is many island chains in between.

So imagine your an explorer, you keep seeing islands, you keep exploring. So that is much more likely.

Lets go further. The waters of the southern tip, horn, or Africa, are among the worst on the planet. This is a very detrimental factor to enthusiasm to traveling further down.

Again, indonesia in a very real way, points to Australia in a nautical way.

Antartica is a plausable thing these islands could be. It could be that they approached it many times, at many different angles of travel, and did not understand that it was the bottom most continent.

Lets go even further. There is no viable food source or fuel source on antartica. So it must be brought there. Since it is on the bottom of the globe, and these peoples obviously encircled the continents, each approach from a different continent, could yield a new large island.

If they were not to understand a globe, then it could easily be that. If you are simply trying to figure out the continent, it would be easy to do that.

The main take away from this map however, is that circular arangement. The continents converge closer to each other in the northern hemisphere, and the southern hemisphere has more open space.

This map shows exactly that.

It would be a case of confirmation bias to assume it is a flat earth because it does not say sphere on the side.