As Explained by Google this is how Media AdsWork:
“With Media Ads, you don’t pick any keywords — the targeting is completely automated. When someone enters a search on Google that our algorithms determine is directly related to your movie title, we automatically display your Media Ad at the top of the search results page.
Media Ads changes the way that you experience video on Google. When someone clicks to play your video either by clicking the thumbnail or the “watch” link, the video expands to the center of the screen and dims the rest of the page around it. The experience is meant to put the viewers full attention on the video and to create a much more theater-like experience.” said Google“
Here’s Screen-shots showing Media Ads: