Evidence?
US Law.
Naturalization is a separate process.
See the US State Department’s Foreign Affairs Manual quoted below:
7 FAM 1131.6-3 Not Citizens by “Naturalization”
(CT:CON-349; 12-13-2010)
Section 201(g) NA and section 301(g) INA (8 U.S.C. 1401(g)) (formerly section 301(a)(7) INA) both specify that naturalization is “the conferring of nationality of a state upon a person after birth.” Clearly, then, Americans who acquired their citizenship by birth abroad to U.S. citizens are not considered naturalized citizens under either act.
“Evidence?”
He came out of the womb of a US Citizen. That makes him a citizen at birth, not a naturalized citizen.
Such is the law, whether you agree with it or not.