Car I don't own comes back to haunt me

This week I got a letter in the mail from the DMV about a car I don't own anymore and haven't for a few years. It was a piece of junk that wouldn't start when the engine was warm and I gave it to a used car dealer to dispose of.. for free. He decided to turn around and sell it to a person who wanted to give it to his grandson. They get in an argument, the grandpa takes the license plates off the car, and he (the grandson) writes the state asking for information on who the grandpa bought the vehicle from. The grandpa I assume, never reigstered the vehicle through the state after he bought it, so it comes back to me as owner, which is fricken NUTS.