Pet peeve: it's salt, not sodium. If it were sodium, we'd all be dead by now.
As for your question, the nutritional label on the can lists the content of the food item as you will eat it, and it is assumed that you will not be drinking the packing water. The beans have most of their salt content from the packing liquid. If you wish to lower the amount of salt that you get from the beans, soak them in cold water for a while before eating them. The freshwater soak will remove some of the salt from the beans via osmosis.