Nugget the Turtle
I don't think there is a punchline in the direct sense. It suggests that Plato portrayed Socrates as much wiser than he actually was because he had an illogical devotion towards him. That probably isn't true, but if you read The Republic, for instance, the dialogues are constructed in interesting ways. Essentially, Socrates will use logic and reason that makes his opponent look like a fool. Meanwhile, onlookers will praise everything he says.
Plato also thought of things in a mystical "world of the forms sense." Wikipedia the theory of the forms because I'm too lazy to explain it. Aristotle brought philosophy back to the ground, focusing on what you can observe. So while Plato is trying to explain reality in terms of pure intellect and a sort of mysticism. Aristotle hits him with a slingshot. Defeated.