Looking at dictionary definitions, I can see where many may claim Manning and Snowden are ‘whistle blowers’.

Its seems the definition allows for subjective reasoning.
Certainly there is no mention of ‘not fleeing’ nor ‘not threatening’.

merriam-webster

whis*tle-blow*er
noun
: a person who tells police, reporters, etc., about something (such as a crime) that has been kept secret

thefreedictionary

whis*tle*blow*er or whis*tle-blow*er or whistle blower
n.
One who reveals wrongdoing within an organization to the public or to those in positions of authority: “The Pentagon’s most famous whistleblower is … hoping to get another chance to search for government waste” (Washington Post).

oxforddictionaries
whistle-blower
noun
a person who informs on a person or organization regarded as engaging in an unlawful or immoral activity.