Yes. Luke, who we know is powerful in the force called out to her. We didn't need to know anything else.Yes. It was explicit exposition. They told us.I TFA we know Rey is somehow force sensitive because of the musical cue in the fight scene at the end, but it is never explained, nor does the movie explain how, earlier, she just knew how to do Jedi mind tricks or use telekenesis to steal a lightsaber from another powerful force user.