I think this map is based on the idea that our world is much larger than we are told. That there are other continents, especially beyond the ice wall. I don't think it requires the belief in either flat or globe earth because either can be larger.

This map in particular has the additional theory of multiple sun's and moons. I think the New Sun and New Moons are supposed to come out of the center. And then over the aeons, the sun and light/dark moons migrate into the outer lands and a new sun and light/dark moon emerges. I think the Mal I saw before was a bit different indicating where the new sun/moon emerges. And it had another layer of continents.

So you can believe in a bigger earth/hidden land without believing in the new suns/moons.

I think the reasoning behind the new sun's and moons was something about ancient scriptures.

And they are local moons/suns in this theory, which doesn't necessarily require a flat/globe earth.