Theory: AT&T has a known relationship with the NSA. Maybe the leak was due to an NSA screw-up. In that case, they're telling a half-truth but wouldn't be allowed to tell the whole truth.
This doesn’t pass the basic smell test. I really don’t want HN to fall down the conspiracy hole that much of the internet now has. It’s eating away at our societal fabric and is wrong 99.9% of the time.