Essentially the two are the same thing, though you may see the terms used in different circumstances. In the U.S., the term "pulled chicken" typically refers to chicken that has been prepared in a barbecue fashion, with a dry rub or Barbecue Sauce. See these Pulled Chicken Sandwiches for a recipe. "Shredded" refers only to the chicken's texture, and is not specific to a certain flavor profile. You could have shredded chicken in soups, tacos, Shredded Chicken Sandwiches, you name it!