If you search for quotes on Google, let's say of famous people like [obama quotes], [edison quotes], [jobs quotes], [president bush quotes] and so on, Google will show you famous quotes from them.
Google doesn't link to the source where they find the quote, so maybe they are licensing a quotes database?
Here are pictures of the quote answer boxes on both desktop and mobile:
This is just another example of a niche Google has wiped out over night by providing answer boxes.
Forum discussion at Twitter.