At the beginning of the book, when Buck was with Judge Miller, he was an important part of Judge Miller’s family. He was trusted enough to walk freely around the property (and even off of it). He played with Judge Miller’s children and often served as a chaperone to them in order to keep them safe. Buck was comfortable and trusting of his environment that when he was stolen by Manuel, the residence’s gardener, he willingly went along with him.
Accustomed to being in charge, Buck initially put up a fight when his new captors