Why does Cassia hold back from telling Ky that she saw his face on the screen at her Match Banquet?

Cassia and Ky talk about their attraction to each other, and Cassia finds she can't tell Ky the truth about her seeing his face on the screen. This shows that even though their connection is strong, she's still holding back. Cassia's eyes are opened to the harsh realities outside her immediate world as she talks with Ky about the screening.