I read it was an "Other Than Honorable" discharge (one notch below dishonorable). Regardless, reduction from Sgt. & OTH discharge or DD would require courts martial rather than Art 15.
'Other than honorable' is still an Administrative (The most severe Administrative, but still an Administrative).
With what he did in that temple. I can only imagine what he was like in the military. They probably gave him and 'Other than honorable' to be nice.