Hyperbole is "obvious and deliberate exaggeration or an extravagant statement." Hyperbole is used to make a point by completely overstating the situation, blowing the statement out of all proportion with the reality of the situation being described.
There are many examples of hyperbole in The Ransom of Red Chief. Consider Johnny's actions towards Sam and Bill in the cave. He's not just talkative - he's constantly questioning, screaming, shouting, laughing, yelling, and making other noises that exhaust and traumatize the adults. No real child would be able to keep up the behavior that Johnny sustains so enthusiastically.
Comic language simply refers to humorous word usage. One example: Johnny lives in the town of Summit - the town is absolutely flat but is called by the name of the top of a mountain.