In the video you can see the game editor that Over the Top Games uses to select the different sets and tweak the light and “mood” of an scene. In the game you will find different basic environments (the swamp, the cemetery, etc.) and those will use the visual and generation parameters they configure in the editor. This way they can make sure that the layout is fully random, but the light and the colors match the style of the setting.
There is more information in their official website.
Check their blog for more info: Fullmojorampage.com