He was accorded the NSA’s top security clearance, which allowed him to see and to download the agency’s most sensitive documents.

Document control works on two dimensions: clearance level and need to know. You need to both have the requisite clearance level and a need to know to be approved for access to a given document. Having a top clearance doesn't mean you get to freely look at whatever you want, although the press and general public seems to think it does.