If you login to your Google Search Console account and click on the Search Analytics, you will vertical line on April 27, 2016 that says "update." When you click on the learn more link there, it takes you to this page which explains Google updated how they calculate some of the search analytics impressions and clicks in that report. Google said there it impacts mobile apps the most.
But John Mueller of Google added that for the first time, the Search Analytics report now includes Knowledge Panel, in various Rich Snippets, and in the local results in Search as impressions when a URL shows up in those places. It seems Google did not count those before.
John wrote on Google+:
We recently made some changes in how Search Console reports & calculates clicks and impressions in Search Analytics.
As a result, you may see a change in the click, impression, and CTR values shown there. For most sites, this change will be minimal. A significant part of this change will affect website properties with associated mobile app properties. Specifically, it involves accounting for clicks and impressions only to the associated application property rather than to the website. Other changes include how we count links shown in the Knowledge Panel, in various Rich Snippets, and in the local results in Search (which are now all counted as URL impressions).
He explained a bit more on Twitter that these local, rich snippets or knowledge panels are only counted when a URL appears in them:
@glenngabe Yes, they should if a web-URL from your site appears in there as a link.— John Mueller (@JohnMu) May 10, 2016
John also added on Google+:
FWIW one question that has come up a few times regarding Search Analytics is how local results are handled. Luckily, it's pretty straightforward: if a URL from your site is included in the local result, it's counted as an impression. If the same URL is included multiple times (eg, multiple franchises in the same area with a shared web URL), that URL is just counted once. If a local result (w/web link) + a natural web result are included in the same results page, then that's counted as 1 site impression (which is used for the view by query, for example), and the URLs individually get the page impressions (which is used in the per-page view).
Hopefully one day we will be able to filter by knowledge panel, local, rich snippets and more.
Forum discussion at Google+.