I'd be more confused about the "fun snack" bit, which doesn't make sense. In answer to your question, it is because that is a general statement about his preference for school or otherwise. The others describe his day. If the text read "George liked school" it would sound strange, like an incomplete sentence as you would be waiting for something come after it. It would also be implicit that he only liked school on that day but says nothing about his general preference for school i.e. if he likes school in general or not. Does that help?