This recipe is a good example of how adjustments are made to compensate for the differences in gluten-free flour and wheat flour.
Binder: The binder is the 6 eggs, which is 3x the amount that is normally in a batch of cupcakes. A wheat flour cupcake would only have 1 to 2 eggs depending on the amount of wheat flour. The egg protein denaturation causes coagulation when exposed to heat. Since protein denaturation is irreversible, when the cupcake cools, the egg remains coagulated, so the cupcake remains intact.
For those who cannot/choose not to eat eggs, an alternative binder like xanthan gum, agar, flaxseed meal, or chia seed can be used.
Hydration: Since eggs are 74% water, the milk was nearly eliminated in this recipe to offset the natural water in the eggs. Butter also contains water, about 18%. So if butter is used in place of oil, the butter is melted. By melting the butter, the water is released and some of it evaporates. This too offsets the natural water in the eggs.
Flour: The amount of coconut flour used is significantly reduced to compensate for the moisture absorbency rate differences between coconut flour and wheat flour. Only 1/2 cup of coconut flour is used in this recipe. A traditional wheat cupcake will have 1 1/2 cups wheat flour. But given the different rates of absorbency, you substitute 1/4 - 1/3 cup coconut flour for every 1 cup wheat flour.