One need not attend a naturalization ceremony to be naturalized. Congress has the power to naturalize people without resort to the ceremony, and it has constitutionally exercised that power in 8 USC 1401 et seq.
Seeing as how Cruz falls into the class of naturalized without a naturalization ceremony, he did not attend a naturalization ceremony.
Congress, as established via Article I Section 8 of the constitution has the full authority to established the rules of naturalization. While that does include your statement above, it includes far more.
It includes the rules for who is able to apply for naturalization, what the ceremony must consist of and it also includes who is a citizen at birth and does not need to be naturalized, i.e. a naturally born citizen.
Some of those rule, in particular those who are born citizens, are described in Title 8 section 1401 of the US Code.