My Teacher Is a Jedi Warrior

I was going through Charlie's school papers (4th grade) and found a math worksheet that he got a very bad grade on. He's never struggled with math, so I looked carefully at it to figure out what they're doing in math that he didn't understand. It was just notebook paper with his responses on it, and he had left all of Section 2 blank.

Me: Charlie! What happened on this math?
C: Um, I don't know.
Me: Did you not understand how to do Section 2?
C: No, I did.
Me: Then did you run out of time?
C: No.
Me: Then what happened? You left the whole thing blank.
C (very earnestly): The instructions said, "Solve mentally."