I read it as Dempsey saying the forces in Tripoli were not told to ‘stand down’ they were told to guard Tripoli. These are the forces that the acting ambassador wanted to put on a plane to Benghazi - and testified as much.
These forces were as far as Benghazi is concerned told to stand down. (but were actually ordered to “stay in tripoli, and guard/do nothing”
Two different incidents. A half truth is as bad as a lie.