Answer: Stacey doesn´t understand why Cassie wants to talk to Lillian Jean.
Explanation:
Stacey knows that Cassie is still hurting from Lillian Jean´s insults, so when Cassie sees Lillian Jean on the walk to school and follows her to talk, and even pretends to believe black people are actually inferior to white people, he doesn´t understand the reason behind it. He doesn´t know that Cassie has a revenge plan.