Google added a note to the data anomalies page noting the Search Analytics data in the Google Search Console may differ. It reads:
Websites only: An update to web search logs analysis. This change may increase the total number of clicks and impressions.
It is simply related to how Google made a change to how they analyze the web search logs. Zienb explained on Twitter, "it is only related to websites, we are logging data differently." "You might see an increase in impressions and clicks," she added.
Here is the tweet when I asked if it was related at all the to app install button change, since they were released the same time.
@rustybrick no, it is only related to websites :) we are logging data differently. You might see an increase in impressions and clicks.— Zineb Ait (@Missiz_Z) December 21, 2015
The update line is on December 14th, so take note, here is a screen shot: