He used to be at the Pentagon. Probably still has contacts there.
I wouldn't put it past him, but if it was him that would certainly compound Newsweak's journalistic and ethical sins, because they described the source as a current "senior Pentagon official".... it would be a huge (though not surprising) ethical lapse to mis-describe the nature of their anonymous source, since they tried to give the claim added credibility by claiming the source was a current "senior Pentagon official"....