This is literal. His dog wakes up and runs off to join a wolf pack. The man is worried that his dog is stalked by wolves. At the end he realizes that his dog wanted to be with wolves and left deliberately. The tracks of 2 wolves, plus the dog, end up indistinguishable from 3 wolves. His dog BECAME a wolf. The man realizes he registered only the danger of the wolves but missed the intention of his dog becoming what he wanted to be -- a wolf. The word "became" is literally something that has transformed or transitioned. The word "came" can mean "arrived" or "returned." The song is not titled "left" "destroyed" "disappeared." It's not about the loss of his dog. Essentially the dog came back to live with wolves and fulfill his desire to live his true nature. Good lesson for anyone during a big change or supporting someone during a change -- don't focus on the danger and anxiety that comes with transition. Focus on becoming the next thing.