"I got out of the truck to have a pee and when I turned around the truck was gone." "Sure, it happened just like you said. Now tell us what you did with all our melons, buddy."
What the hell can you say to that? You don't want to say MONSTER because no one will ever believe that. So you have to come up with a lie that sounds just as stupid as the truth. I would have just have been better for everyone if they guy just got eaten along with the melons. Good thing for him that the monster is a vegetarian - well vegies and truck parts.
All you really can say is that you had a wicked craving for melons and didn't know when to stop. Then get another job in another state delivering pumpkins.