After a lot of thinking and the events that happened in episode 2, I think Luke did (and God forbid) abandoned the group and here is my reason why he would've done that. He saw Carver and his gang and decided to high tail out of there without thought of the others. The reason why he would want avoid Carver so badly is because Carver is his Father. Luke was having the hardest against Carver because Carver wants Luke to be just the type of leader he is, and Luke doesn't want that. So, taking the advantage that he's the son of Carver, he and the others escaped by letting those scouter's guard down, knowing that Caver fully trusts Luke.
Here's something that connects with the theory about Carver's past. Caver before and after the Apocalypse was a good man. Everyone that knew him loved him. He had a wife and two kids (one of them being Luke and the other an unnamed daughter). During the Apocalypse, Caver became the leader of a group that later grew into a community, and Caver had always told Luke repeatedly that he would be the next leader of this new Civilization when his time of death had came. One day, a pack of bandits had invaded the community, killing anyone that got in there way while stealing supplies. The wife and daughter were happened to be some of the victims. After that, Caver never seemed to be the same man he was before. He had grown to be more cruel and abusive towards others. Everyone feared him or even hated him. Luke started to fear his father too, and Caver started to teach him the new ways of being the leader he is now. Even so, Caver still wanted Luke to become leader when he passes. Luke, wanting to avoid this, decided to run away.
This is also why Luke treated Clementine so nicely, she reminds him of his dead sister. Also that is why moves on so easily, so that he won't lose his sanity like his father did. It is also why he looked up to Uncle Pete as his Father figure, Caver became a bad man. Even so, he may have adopted a few things from his father when he was good, as shown to having pretty good leadership skills possibly being taught by him.
When Luke states that he has lost his folks, he may have been referring to his mother and sister's passing and father not being the same man.
When Luke says that family is the important thing in life, he looked a little sad knowing that his family is gone.
Anyway, that's my theory. Let me now on your thoughts on this to see if you agree or disagree, and be sure to keep it friendly too.