Because he saw Su Ziyan had changed into a very conservative set of pajamas.
How conservative?
Not even her wrists were showing!
Qin Yu was utterly disappointed, no wonder his well-behaved wife had pushed him into the bathroom, so she was just changing into her pajamas!
Damn it, if only he'd been quicker, if only he hadn't been admiring himself in the mirror!
A smile played at the corners of Su Ziyan's mouth. "Nice try, scoundrel, but don't think about taking advantage of me!" she thought as she walked towards the window and with a swoosh, drew the curtains closed.
Qin Yu was very adaptable and quickly came to terms with reality. The initial shock of entering Su Ziyan's room had been so great that he hadn't checked for pinhole cameras or recording devices.
Now, Qin Yu had gotten a bit more comfortable and started looking around.
Upon inspecting, Qin Yu indeed found something amiss.