I think I understand why you’re confused.
Note that our documentation contains all articles we wrote, but it is filtered depending of the theme you’re using.
On the top of the page, you can select the item. Please find the attached screenshot. Then, it will automatically filter and hide all articles that don’t concern the item you’re using. For exemple, in the category you’re referring to in your first message, there is no article related to Gwangi. This is why this category is empty for you.
When visiting our documentation, you need to start from the homepage: https://doc.themosaurus.com/
There, all the categories will be visible only if there are article in it that concern your item.
Hope this will help you better understand how our documentation works. Let me know if you need anything else.