NSA grabs everything, almost all of it innocuous garbage intel wise. The computer scanning would have flagged DCIA's communications based on key words, phrases, recipient, and other factors before being brought to the attention of human eyes.
"Say babe, how about we knock some boots tonite". Doesn't strike me as a red security flag with a Drudge Siren.
Real question is was Petraeus under constant surveillance, routine. Scheduled scan, event driven (Benghazi), command driven (O wants to gauge loyalty of flag officers pre-election)
I suspect that the real time monitoring of the Benghazi assault and the stand down orders caused a flurry of encrypted msgs among general staff with an angry WTF tone) The knock down of Petraeus was a message to every flag officer, "Four stars don't mean shit, we own your ass! STFU!"
Reminds me of Admiral Ham being removed from active duty.
Where is Ham, anyway.