Odd Language #184: When Retired?

“The Army investigation was ordered by the head of U.S. Central Command, whose commander at the time was retired Marine Gen. James Mattis, Trump’s pick to be defense secretary.” — http://www.nbcnews.com/news/us-news/trump-pick-advisor-inappropriately-shared-classified-info-n695866

The issue: Was General Mattis retired at the time he ordered the investigation? Presumably not since the U.S. Central Command is military, but imagine if he had been head of something else. He might have already retired at the time he ordered the investigation or might have retired after that.