There seems to be some confusion over this story. It did not originate from the Guardian, but from the Observer. The Guardian must aggregate or something stories from the Observer. They've taken down the story while the Guardian editorial board can investigate it. Greenwald has nothing to do with the story.
Source: Glenn Greenwald's Twitter feed. Make sure you select "All Replies" if you're on the desktop website.
https://twitter.com/ggreenwald