Technically, if you're measuring surface area, it' important to remember that the earth is not a sphere. There's a bit of a paradox measuring shorelines: the shorter your ruler, the longer it gets, because you're able to capture more complex features. Pethaps the authors took an extremely precise measurement of the surface of Estonia, counting everything down to the sinus cavities of dogs sleeping in alleys...

Area isn’t notably affected by fractal boundaries. Only perimeter is.