This is most likely because this category is a subcategory, which means it will inherit the display setting of its parent category. So if a subcategory is set up as a grid but still displays as a list, check the parent category to see if it's set up as a list. At this time you do not have the option of using different displays for parent categories and their subcategories.
To edit a category:
- Log in to your CoreCommerce admin panel
- Hover over the Inventory tab and then click on View Categories
- At the bottom, under the Display section, you will see the setting to display as either a grid or list