Abhi this really depends on the website and the author in terms of attribution. In some cases, the author "sells" the article to the website for a one time fee. In others, the original author retains attribution and rights of usage, but licenses that particular blog to use it as a way of putting their work out there for others to discover.
For example, a lesser known author can write a story for a well known blog as a means of increasing their scope and reach.