The bat site on the page you refer is displaying a 'Story Map Series' on the section of the Story Map Journal. So a story map within a story map. This is done by using a 'Web Page' not a 'Map' as the content in the journal section. (if that makes sense)
To do that:
1. Create a 'Story Map Series' story map with all the maps you want to display. This will be referenced by your Story Map Journal
Open the finished 'Story Map Series' story map in view mode (not edit mode) and copy the URL.
2. In the Story Map Journal you need to add a section and the main stage content will be a 'Web Page' . Paste the URL from the above.
Done.
regards, Mark