You can read that blog post here.
The DCoE also offers an excellent PTSD fact sheet that expands on that blog post. For example, it answers with the following on why, if PTSD is clinically legitimate, every person ever exposed to trauma is not afflicted:
Fact: While it’s true that only a percentage of people exposed to trauma develop PTSD, this is due to several specific factors. Each individual exposed to a trauma has their own set of risk factors for potentially developing PTSD, some of which are genetics, past history of other traumas and the degree or duration of their exposure to traumatic events.Have a look at the DCoE PTSD fact sheet here.