The principal heading concerns an indefinite subject, but the final part notes that other sentence constituents can likewise be indefinite for purposes such as individuality, type, magnification, or slightness.
وَاللَّهُ خَلَقَ كُلَّ دَابَّةٍ مِنْ مَاءٍ
And Allah created every moving creature from water. (Al-Nūr 24:45)
«مَاءٍ» is not the subject: it is governed by the preposition «مِنْ». The source discusses its indefiniteness with reference to kinds. The rhetorical interpretation of definiteness and indefiniteness is therefore not limited to grammatical subjects, even though this chapter begins with the subject.