Can you not “resign” your commission?
Further down in the story is this:
“The New York Times reports that the new Defense Secretary, Ashton B. Carter, asked for Kirby’s resignation. Sources close to Carter say that he has “expressed reservations about having a uniformed officer represent the Defense Department in its daily dealings with the news media,” and will likely replace him with a civilian. (No replacement has been announced yet.)”
If you are asked to resign your job, you submit your resignation. It is resigning as PAO, not resigning his commission.
Until we learn what he REALLY did, I’ll just consider it a case of tomayto/tomahto.