OK, that's the NSA, you can assume they know everything already. And in this case, the article mentions Yahoo, which is where the information was in the first place.
Indeed! The discussion is about rogue elements getting a Buddy List that was in AOL's hands, and therefore one should assume the TLAs already had it. Google might not have, unless you, or all your contacts, used the AIM/Google talk integration that existed for a bit, in which case they had it. Leaving aside that it's quite likely these connections already leave a Google-based data trail.