I think the draw was overdone. It was just meant to show that she was shocked the Woojin was showing some respect and manners to her by calling her noona.
If I'm not mistaken, noona is a kind of honorific term for females that means older sister and that you use to call someone you respect and admire. If you remember, Woojin was always very informal, borderline rude towards his friend and this would be the first time he uses the term with her. That's why she says that Hwon must be a good influence on Woojin after all ( what he is ... remember that Hwon always tried to make sure Woojin was goind to school when he was with him, etc).
That noona's face creeped me out