I would rather read the Constitution. Article I gives Congress the power to establish naturalization laws for the country. How can Congress establish laws on who needs to be naturalized unless they first establish who doesn't need to be naturalized, i.e. who becomes a citizen at birth?
They don't and can't "establish" who is a natural born citizen. They have to use the existing definition, whatever that might be. Then they can say other people are citizens, at birth, or after birth following some procedure. But either way, they are not defining "natural born citizen". They have no power to do that. They only have the power to define uniform rules of naturalization. Thus anyone who is a citizen because of or as a result of an act of Congress is a naturalized citizen.
The power to define the terms would be the power to change the Constitution, and that Congress cannot do, except through their part of the amendment process.