It's really dumb.
NSA grabs all data that flows over all connections.
There's an HTTPS session between the user and the Gmail server. When writing/reading drafts, data is sent back and forth between users and Gmail server over network.
The email does not have to be transmitted from one SMTP (mail sender) server to another, in order for the content to have already passed over the network.
Moreover they may have other ways of spying on content that's in the clear in device memory, when the user is reading/typing on their device, without even having to decrypt it.
These people are stupid.