Continuity mistake: When Arnold is sitting in the kitchen with Dino's personal stuff, Grandpa offers him a shrimp cocktail, and Arnold turns his head to look at it. In the next shot, he is suddenly looking inside the box. (00:06:45)
Audio problem: When Arnold says, "It's almost like Dino left his whole life in my hands," as Grandpa responds with, "Not his whole life," his mouth doesn't move until the word "life." (00:06:58)
Answer: No, he did not. He is seen getting off the bus with a suitcase, so he must have not been home for a few days so there is no way he could have known.
Bowling255 ★