The study's conclusion clearly states that rape-induced PTSD tends to cause HPA-axis dysregulation, resulting in depressed cortisol levels.
This is what the study says in the "Background: section...
In chronic sexual abuse victims with post traumatic stress disorder (PTSD), the hypothalamic pituitary adrenal (HPA) axis can be dysregulated. In single rape victims, PTSD symptoms are hypothesized to function as a chronic stressor leading to similar HPA-axis dysregulation.
They concluded what they hypothesized.
Feel free to reference my post #187, where I point out that you completely ignored the sentence linking single rape events with the same lowered cortisol.