It's likely a play on words combining the physical gesture of a nod with the concept of verbal agreement.
Here's how it might be used:
* Instead of a literal nod: Someone might say "I understand," "You're right," or "Agreed" as a verbal way to acknowledge a point.
* Emphasizing agreement: The phrase could be used to indicate strong agreement or understanding, perhaps even with a bit of humor.
While not a real phrase, it's a playful way to express agreement or understanding, often used in informal settings.