He's assuming it was spontaneous and not something she's been thinking about. She's more thoughtful than she might let on; life is not an eternal playtime for her. Far from. And he's worth thinking about.

She listens to him because he's worth listening to. What's of value to her is for her to determine, and he's at the top of the list. Hoping she wouldn't be paying attention to what he says was wishful thinking of the most realistic sort. Maybe she didn't have to make such a big deal out of it; quoting someone else is perhaps not directly a great feat. But for her, it's the thought that counts. He thought about her enough to see something of her in those words, and to remember them. He thinks enough of her to share a lovely sentiment. In that light, it's quite a grand romantic gesture.

"Never," she assures him. "You wouldn't get to be around me so much if you had no good qualities of your own."