This is actually Civil Service slang, and the question could maybe have pointed this out. It could also have pointed out that the word is borrowed from Muslim and Hindu cultures (where, as of course you know, it refers to the religious and social practice of female seclusion).
According to Wikipedia, "Purdah has been imposed in ministerial guidance since at least the early 20th century reflecting an earlier 'self–denying ordinance', and has considerable moral authority, its breach carrying with it in worst cases the possibility of actions for abuse of power and misconduct in public office."
Wikipedia doesn't mention broadcasters, or other news media. It does mention social media: basically, civil servants are allowed to post factual information but are urged not to post anything political.
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