The issue is that we're not privy to the editor and their motives or the strength of Greenwald's evidence. It could very well be that he has a solid story. In this case you have a well known journalist claiming that his editors are censoring him on an important story.
The editors can run the story with a disclaimer outlining their concerns as Greenwald argues.
The job of an editor is literally to make decisions about what to publish, not to publish everything or kowtow to celebrity journalists or potentially big stories.
The editors can run the story with a disclaimer outlining their concerns as Greenwald argues.