Cheerilee bites her tongue before she can say anything more. In the span of this brief conversation, she figured it out. Twilight is giving Anon everything he could ever want. She's given him protection thanks to her status, she's given him friendship with ponies that will make professionally tailored suits for him, and she's given him an entire freaking house. For free. Of COURSE he acts nice around her! Meanwhile, why would he need to hide his true self from his teacher, who has nothing of the sort to offer him? THAT'S what he's really like.