He's been hungry so long that he's forgotten the taste of food. He cannot eat the animals he sees -- the rare animals he sees -- because of all the things he's hungry for, companionship is more in demand than physical needs.
It's not until he looks up and sees the sun that he learns hunger; Sanzo takes him by the hand and leads him off the mountain and feeds him. As he devours, as he tears into the food with a stomach wakening again to need, Sanzo has few kind words.
Goku basks in the violence, basks in the smack upside the head and the verbal abuse; it feeds something in him that has been emptier than his belly.