Recipe(tried): Gingered Sweet Potato Pumpkin Soup

This morning I searched some of my cookbooks in an effort to recreate the wonderful Gingered Wild Yam & Pumpkin Bisque my husband and I enjoyed at a Cuban restaurant last week. I found a Ginger Pumpkin soup recipe and tweaked it. Does anyone know what makes a bisque a bisque, as opposed to a soup? Can you just call any thick cream soup a bisque? We think this recipe is pretty close to the dish we had. From what I gather in my reading, most of the vegetables sold as yams here in the states are, in reality, sweet potatoes. The addition of the sweet potato made this a much more orange colored soup than the one we were served. Perhaps wild yams are lighter in color, does anyone know? And/or the restaurant soup may have had a lot more cream or milk in it. Here's my current version, in case anyone is interested in trying it.

GINGERED SWEET POTATO PUMPKIN SOUP

One 2-pound pumpkin
1 onion, stuck with 2 cloves
3 cups chicken stock (next time I will use veggie stock as the chicken flavor was strong)
1/4 teaspoon cinnamon
2 Tablespoons finely chopped fresh ginger
1/2 teaspoon ground pepper
1 large sweet potato, baked or steamed until very soft, peeled
salt
1/4 cup heavy cream
1 can evaporated skim milk
1/4 -1/2 teaspoon cayenne pepper (or more, to taste)

Peel pumpkin, remove seeds and stings, cut pumpkin flesh into 2-inch pieces. Place in large saucepan with onion, stock and seasonings except salt. Bring to a boil. Reduce heat and cover, cooking slowly until pumpkin is soft. Remove onion and cloves and discard them. Puree the soup with the sweet potato in a food processor or blender. Taste for seasoning, adding salt and more pepper, if desired. Return soup to pan and mix in cream and evaporated milk. Heat through. Stir in cayenne. Serve hot.