The only person who probably really understood her (apart from her father) was Ginny Weasley and probably then only half as well as she understood herself. She was a bit like a rare animal out in the habitat. That would explain why she caught him staring at her. Generally when she stared at people, she made it look like she was just staring off into a space. Luna was pretty good at making people think she wasn't paying much attention at all.
Her eyes lit up at the announcement that there was pudding. She got up to her feet, she let out a "Ooh!" of excitement and wandered over to where he was. "I make the very best pudding." And she could use some chocolate. "Do you want some?" Because she could eat the whole thing, let's face it. But she'd be nice and make him some if he wanted a bit.