well grayson doesnt know exactly how it all went down so his explanation is how he sees it. the car was taken in for safe keeping so it wasnt impounded technically but the police didnt know where else to put it. the reason it was auctioned off is because it was confused for evidence which, generally speaking, can only be held for 5 years if there arent any charges which there obviously werent.
i hope that clears things up finally.