when your website become so popular and has lots of active users and content
the result is more indexed pages by google then
first google show the most popular of your page as yo can see in your image, some how like a table with 2 column and 3 row
and after that because you have lots of data on your site like
w3schools.com or stackoverflow.com it brings a customized search box under the title of your site, so the result of the search will be limited just to that website
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solved Is this par of SEO or its paid to google