How does Krakauer contrast the “Alex” that Westerberg knew with the “Christopher” his parents knew?

Westerberg's Alex was hard working, willing to do anything, and he enjoys being in Westerberg's home. Alex enjoys the social aspects, and even the jobs he previously would have rejected. Alex considers Westerberg's "home". Alex continues to communicate with Westerberg after he leaves Carthage.

Alex rejects his parents' home. He keeps to himself, rejects the financial help they have to offer, and when he leaves.... he cuts all ties.