Gelatin is made from pork by-products, among other things. It's made from animal by-products like bones and hides, and a small percentage of "other" by-products.
Gelatin is derived from the collagen found in animal bones. It may be gathered from common feed animals such as cows and pigs. It is possible that a specific type of gelatin is made from the bones of a pig therefore it would be acceptable to say that gelatin is made from pork.