Compare § 13 of this Lecture, where Cyril seems to refer especially to the heresy of Manes, as described in the Disputatio Archelai, cap. 6:  “If you are desirous of being instructed in the faith of Manes, hear it briefly from me.  That man worships two gods, unbegotten, self-originate, eternal, opposed one to the other.  The one he represents as good, and the other as evil, naming the one Light, and the other Darkness.”