How the catalog of Category Community is displayed?

Summary:

We have created a Category community with 31 topic communities added as catalogs inside the Category Community.
As a learner, when I am directly using the Self Service link to access the Category Community, I see by default 4 items(4topic communities) being displayed in the quick carousel under Catalog. We have not marked these 4 topic communities as Featured at all. Wanted to understand how does system decide which 4-5 items to show in the image carousel?

Content (please ensure you mask any confidential information):

We have created a Category community with 31 topic communities added as catalogs inside the Category Community.