Quinn knows a lot about Santana. She knows what makes her happy, what makes her angry, and what makes her sad. She knows what her favorite restaurant is and what color her favorite hair tie is; so it's understandable for Quinn to feel confused when she sees Santana sitting next to Karofsky scowling and wearing a shirt that says she's Lebanese when Santana is clearly not, after all, Lopez is a Spanish name.
When she's done rehearsing she confronts Santana, wondering what the shirt means. What she gets as a reply does nothing to help her confusion.
Why would she hope that Fabray is Lebanese too?