Yes, u are right...it is obvious. Don't be confused by "Who is him" ? imagine you are kissed in the darkness. of course you will be shocked. but it is Dan Zi who kissed Kai in the darkness. Actually Dan Zi got very upset afterward. He can't be sure if Kai would love him or not..
Reading it a second time I finally get it Danzi kissed Kai but, since Kai could not see very well since it's dark he doesn't know who kissed him