Somehow I don't think even the NSA's system is going to pick up on the fact that it's an attorney-client conversation. The conversation itself would not be admissible in a court action, but if the NSA were looking for known "confidants" of the flagged terrorist suspect then it wouldn't be surprising that the Visa was flagged for cancellation by one of those automated NSA algorithms.
NSA lives in a world where they don't normally have to worry about attorney-client privilege because they're not trying to bring cases to trial, they're trying to gain intel on enemy networks, and ideally prevent them from gaining entry to the U.S. in the first place. So I'm not even sure if attorney-client communications is something their analysts would even check for (that is, if a human analyst even ever saw this conversation).
NSA lives in a world where they don't normally have to worry about attorney-client privilege because they're not trying to bring cases to trial, they're trying to gain intel on enemy networks, and ideally prevent them from gaining entry to the U.S. in the first place. So I'm not even sure if attorney-client communications is something their analysts would even check for (that is, if a human analyst even ever saw this conversation).