Google trends closely follows the usage of the word in the media.

The reason the Trends chart jumps after the election is because that's when the larger public learned about what is going on, and people were trying to figure out how it happened.

Pre-election examples from a quick search:

http://thehill.com/blogs/ballot-box/presidential-races/30074...

https://www.theguardian.com/technology/2016/aug/24/facebook-...

http://meta.mk/en/macedonians-from-veles-open-propaganda-web...

http://money.cnn.com/2016/10/30/media/facebook-fake-news-pla...

http://fortune.com/2016/10/12/facebook-fake-news/

http://thehill.com/policy/technology/296211-facebook-steps-u...

and countless more...

They picked two stories for explaining the loss and pushed them extremely hard - this and the Russian conspiracy stuff.

Both stories share one salient characteristic - if both were reason for the election loss, neither the Democratic party nor Hillary could be blamed for it.

It is unlikely that news media that aligns with and donates money to the Democratic party are going to run stories about how Hillary was a terrible candidate who shouldn't have been allowed to run in the first place any more than Fox News might suddenly start supporting Democrats one day.

Fake news was a huge issue before the election. People I know were discussing it daily.

Of course the Democratic Party talked about it after the election. What else would be expected? Many people who were paying attention were talking about it before that as well. You should read those articles I posted.

The Democratic Party and its candidate had problems, but that doesn't diminish the role of fake news.