OK, I've got to add my opinion on this since my last name is Torres and my very big Hispanic family, complete with husband born and raised in Mexico, gives me some cred.
First of all frijoles negros (black beans) are as much a staple as pinto beans in authentic Mexican food. Pinto beans are more common in American/ Mexican restaurants and maybe refried beans are associated with pinto beans simply because they are served more frequently in the US.
I make many Mexican dishes for my family. My Mexican MIL lived with us for a few years when she moved here over 16 years ago and taught me all she knows. I have a great interest in cooking and absolutely love learning how to make authentic dishes.
Cooking beans in clay pots do bring out the best flavor, but the trick to great beans is adding slivers of garlic and onion to the cooking beans, be it black or pinto, and adding bits of bacon will make them REALLY good. Make sure you keep adding water and in about 2 hours your beans will be perfect. You can eat them in a soup style plain or by adding pico de gallo ( chopped tomato, cilantro and onion). To refry just heat up your pan nice and hot with oil, lard or bacon drippings and add the strained beans and let them fry!! Get a masher and just mash the beans and then let them simmer and thicken up. Serve them with some cheese on top and those are GREAT refried beans, black or pinto!!
