Either is correct, but they have slightly different meanings. "George likes school!" - George likes school in general. Not just today, but every day. "George liked school!" - George liked his day at school today.

'George likes school' is talking of what Georges opinion is now, at this moment. The inference is George is still at school. 'George liked school' is talking of what George's opinion was in the past. The inference is George is no longer at school.

It says this because George still currently likes school! He did all of the other things in the past but him liking school is an ongoing action. It would not be wrong if it said “George liked school” but it would be specific to that day rather than a general statement that he likes school.

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?

Either is correct, but they have slightly different meanings. "George likes school!" - George likes school in general. Not just today, but every day. "George liked school!" - George liked his day at school today.