Category is the single Ingredient Category (Proteins, Vegetables, Dairy...) managed under Settings > Kitchen Settings > Ingredient Categories; it drives the category cards, the category filter, category counts and the "Report by Ingredients Category". Sub-recipe Categories is a multi-select of your meal categories (grouped by meal category group). Tagging an ingredient or sub-recipe with meal categories lets you filter the Ingredients list by those meal categories in the sidebar. Sprwt saves the meal-category tags separately from the ingredient category.