Just like any other company that has a community edition and a paid version. (See owncloud or nginx) As author he is at liberty to publish his own product unde

Just like any other company that has a community edition and a paid version. (See owncloud or nginx) As author he is at liberty to publish his own product under whatever license he wishes. And if he wants to sell a "enterprise" version under a proprietary license he is free to do so.