Force of habit. She was trying not to let the humans find out who she really was, after all. An act, she had learned, worked better if she was consistent about it.
It didn't escape her notice that he left off his own name. A lot of people, demons, and other things were picky about naming Names. Words had power, and Names no less so. Giving out your Name could give someone power over you. Luckily, the name "Ruby" wasn't all that special.
"Maybe because I just clawed my way out of some oubliette not that long ago," she said, "Just a little hole-in-the-wall called Purgatory. Maybe you've heard of it?"