Chances are this was nothing but the typical deny first and don't bother checking later policy that government agencies (especially intelligence services) have WRT to FOIA requests. The CIA has it down to a science. Last year somebody filed a lawsuit after they responded to a FOIA request for nothing more than their FOIA policy and they responded saying their were no documents matching the request.
Now keep in mind every agency publishes their FOIA policy publicly so the only way someone whose job was processing information requests wouldn't find it is if they didn't look. In fact that was the point of the request - irrefutable evidence the CIA is actively ignoring the law like everybody knows they are. The NSA certainly does the same thing.