Well, I can only guess. You should probably ask the people who made this web site for a definitive answer.
There several plugins which display a list of posts of certain categories via shortcode. One of these plugins is http://wordpress.org/extend/plugins/list-category-posts/ . Another one is: http://wordpress.org/extend/plugins/display-posts-shortcode/ .
You can place the category list shortcode inside the accordion shortcode. For instance:
[accordion title="podcast episodes"][cat totalposts="10" category="2" thumbnail="false" excerpt="false"][/accordion]
[accordion title="posts in category 1"][cat totalposts="10" category="1" thumbnail="false" excerpt="false"][/accordion]
There are also other accordion shortcode plugins e.g.:
The lists on that page (which you have mentioned above) contain only the podPress player elements because their podcast post contain no further content.