Cruz wasn't naturalized.
People born overseas to a parent citizen are citizens at birth.
If you mean that he didn't participate in a naturalization ceremony, I agree. Infants aren't capable.
But case law on the subject of a citizen-at-birth, born abroad of one citizen parent, affix the label "naturalized" just the same.
Bellei obtained his citizenship the same way Cruz did. SCOTUS said "A person born out of the jurisdiction of the United States can only become a citizen by being naturalized," and "Bellei, as a naturalized American, is entitled to all the rights and privileges of American citizenship, including the right to keep his citizenship until he voluntarily renounces or relinquishes it."
Mr. Bellei did not participate in a naturalization ceremony.