Hi Phil,
Milk is fairly high in lactose (a natural sugar) and so the carb count is quite high - for example, skimmed milk contains about 5g of carbs per 100ml. The lactose content of other dairy foods is a bit lower and therefore the carbs are a bit less - for example, single cream will have about 4.1g of carbs per 100ml and double cream about 2.7g.
There are 2 factors to be considered:
Generally, you would only eat cream in relatively small quantities, say a couple of tablespoons at a time and therefore, your portion size and carb count is smaller than drinking a glass of milk which may be 200ml or more.
As cheese, cream, butter etc are higher in natural fats and proteins, this means that the lactose is absorbed more slowly and hence, will not make your BG rise in the way that drinking milk would.
Hope this helps.