If the will of Congress, expressed in a statute, was that children born in Cambodia, of Cambodian parents, are citizens of the US at birth (and it is ludicrous to think an infant is competent to participate in a naturalization ceremony), such an Act is valid under the power of Congress to naturalize. By your rule, these persons are NBC of the US. But your rule is not the one that operate in the law.
By the way, those hypothetical Cambodians would, as a matter of law, be citizens of the US.
We can look to the constitution, which contains the will of the founders. Art IV, Sec. 2 says that a person who is a citizen of a state is at the same time a citizen of the US. By your rule, Congress could change this, too, by Act of Congress.
You assert that Congress has the power to natualize and that that power is limited to naturalization only.
That is not what the Constitution says. Allow me to quote the section directly from Article I Section 8:
To establish a uniform rule of naturalization, and uniform laws on the subject of bankruptcies throughout the United States;
“A uniform rule of naturalization” includes but is not limited to, who is a citizen - by birth or by naturalization. A citizen at birth is naturally born a citizen.