I think fake news is a term that's been floating around a while. The media and the DNC used it to try and discredit trump's election won and now that crazy arsehoke Trukp has taken their balk and run with it and just uses the term to challenge pretty much any statement or fact they challenges his position.
Fake news has existed forever but it's the media and DNC who brought it right into the public consciousness and it's Trump who turned it into a marginally less childish way of saying fraud not.
Fake news has always existed in fine shape or form, but it's only recently that it has become an excuse.