In my honest opinion, I think that's it. I think that could be the end of the story and plot following Clementine and that final scene is there to maybe illustrate something to us. It's that, people die in this new, ravaged world, but life goes on shown by the two people walking. Clementines look of unease is a connotation of her memories and thoughts of Lee, as Lee always told her not to trust strangers. What had just happened? She was manipulated by campman (a stranger) and Lee rescued her. I think that event really drove home to Clem to be wary of strangers or people you don't know.
I don't know, many people could disagree, Its only a theory. However what if that is the end? Just showing us that Clementine lives on, and so does the rest of the world. Of course, maybe im wrong and it is Omid and Christa, which I do really want, but.. You never know with The Walking Dead.