This recipe calls for first frying the sausage until fully cooked and then poaching it in pasta water. Many other pasta recipes from this vendor use similar technique. What is the goal here? Is it to improve the texture of meat, imbue it with some "pasta" taste or make kale taste meaty? Is it important to use "starch" water? 
In my experience, a 400 gram can of beans contains about 240 grams of drained beans. That will vary slightly by the type of bean. 