Rewards can be either instinctive or social. Food is an instinctive reward. Interaction is a social reward. Whilst you can form a relationship with a dog using food, this does not mean you have formed a friendship with them.
You will notice that when Scooby is offered food, he is almost obsessive and totally unaware of my presence. His body language shows extreme tension, particularly around the base of his body. This is because food is an instinctive reward. There is no thought process. It is simply a reaction to the presence of food. It is a survival instinct.
But when no food is present, after a short time, he seeks interaction. You’ll notice his body is relaxed. Scooby inviting interaction with me is a response, rather than a reaction. He is thinking about the situation. Given time and space, he accepts my presence by marking my body and the surrounding area. Acceptance of my presence now enables a friendship to develop.