Luna knew exactly where the group was, however Joe didn't seem to be on a direct path back. She didn't say anything about it however, and decided not to unless they were starting to stray away from everyone else. She figured he's smart enough to find his way back. Basically, he isn't as useless as he makes himself out to be. It was funny that he thought she'd find leaving him easy in the end since Luna knew how she was. Simply leaving someone behind isn't something she'd normally do. "I'm Luna. Nice to meet you. Well hopefully he isn't too angry with you."