It's perjury if the term "confidential source" legally implies it was information conveyed by a human informant instead of gathered by electronic surveillance. The definitions I can find online say that "confidential source" is synonymous with "human informant" and must be a person. While this might be a "legal person" which includes a corporation, it would be a stretch to call a Stringray a person.

In my mind, they are simply lying about an illegal wiretap, and "this has not been challenged" only because the lie was taken as truth. But I'd guess the exact phrase was well-crafted by a lawyer who thought this alternate "plain English" interpretation would work as a defense. I'm doubtful a judge would view this charitably, but as you say, a prosecution where we find this out seems unlikely.