Parents Day - S5-E6
Continuity mistake: In the scene where Arnold's parents leave for the last time, Grandma's hair is dark at first, then it becomes purplish-gray.
Parents Day - S5-E6
Continuity mistake: In the tricycle section of the last event, the chinpiece of Helga's helmet keeps switching colors.
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 ★