He would have written cityons naturels, but sometimes things are just understood in the context of the paragraph. In that case the paragraph/section was talking about Citoyens/Citizens, so that is what the adjective "naturels" had to be modifying (in the grammatical sense, as El Lobo Azul, (meaning the Blue Wolf, with Azul modifying Lobo) . It was certainly not modifying "subjects"/"sujects", which does not appear in the section.