Whistleblower is commonly understood to uncover illegal, criminal or otherwise punishable activity within the organization, that is being hidden. Thus the metaphor of "blowing the whistle" - as in, attracting attention to something untoward going on. However, just releasing secret documents which do not contain the proof of any specific criminal, or otherwise untoward, behavior is not "whistleblowing". For example, Manning released 251,287 US Diplomatic cables and 482,832 Army reports - unless you consider the whole US Diplomatic corps and US Army to be a criminal enterprises, this goes way beyond whistleblowing, as described above.