Nowhere in the constitution is freedom defined, or even mentioned. Our constitution lays out the governmental structure of our republic. Only in the first amendment of the bill of rights is freedom mentioned and then only with regard to protected classes of communication.
This may come as a shock, but rights were assumed to be natural and God given by our founders (read the Federalist Papers). No where in any U.S. legal code is the authority to create or define rights invoked. Furthermore, the basis for the decision discussed in the article was given as international standards of "human dignity", not the U.S. constitution.