Apparently he hadn't misunderstood at all. Because she was kissing him back. It definitely occurred to him that she kissed him back because she wanted to, not because they were pretending, and that made it all the more amazing.
He was a little disappointed when she pulled back, but cheered himself with the thought that she probably wouldn't mind if he did it again sometime. Of course, that was nothing compared to how he felt when she told him that she'd liked him since last term. He'd had no idea, obviously, assuming that she was way out of his league.
"Loads cuter? Really?" he asked a little stunned, because he really didn't think he was much to look at. It seemed impossible really, that she'd like him out of all the blokes she could have fancied, both wizard and Muggle, but he wasn't about to question his luck. Instead he leaned down and kissed her again.