You wouldn’t call seaweed vegan. Seaweed is seaweed all by itself. It’s a plant.
You wouldn’t call tomatoes or blueberries or nuts vegan. They’re plants.
RECIPES are vegan or not vegan, animal-free or animal-based.
If the recipe contains no animal products, it’s vegan or animal-free. If the recipe contains some part of the animal, then the recipe is animal-based.
If it’s all plants, then it’s vegan, animal-free or plant-based, etc.
Even if it’s part animal and mostly plants, it’s still considered, as a whole, an animal-based recipe.
The steamed peas I had this morning were not vegan, because I didn’t do anything to them, besides steam them.
If I had put oil and garlic on them, then they’d be considered animal-free or vegan style, meaning no butter or animal product or animal flavoring was added in the preparation of the peas.
If I added butter, milk, cheese or chicken, then they’d be considered animal-based.
Blueberries by themselves are plants. Blueberry pie is either vegan or not vegan, animal-free or animal-based judging by the ingredients put into the pie crust and the filling.
The point being made here is that vegetables, nuts, fruits, grains, legumes etc. are plants until such time you alter them by making a formula or recipe with them, and then the formula or the recipe made with the blueberries etc. either contains animal products or contains no animal products.