We don't know what the FBI is telling the judge now. The affidavit above is from November; it's what got the FBI he original stay. The document explaing the reasons for requesting an extension of the stay is classified and has been sealed.
I don't think the affidavit alone. There was another sealed delivery to the Judge in January I recall, then he issued the stay. As I recall the Judge's comments, he wasn't exactly thrilled.
I can bet what the FBI said - all sorts of super-duper secret stuff is going on, just as vague as the affidavit, maybe less so, signed by a bigwig that impressed the judge. And since the judge doesn't get to keep the document, the writer can say pretty much as he pleases without risk of contradiction later.