If Rey noticed any difference from how she usually addressed him, she didn't show it. All she knew was that she wasn't coming to Luke now as a student. She was coming to him as a concerned friend. Friends don't usually refer to one another by titles.

His words didn't immediately make sense to her, but then she realized she had to look at it from his point of view. Which was, she knew, ridden by guilt and shame, most it not all of it being wholly undeserved. "Snoke created Kylo Ren," she told him evenly. "You were just trying to help your nephew. What he became was out of your hands."