Step-by-step explanation:
Sarah was surprised that Adnan had asked to Jay for getting a gift, because it was rather natural that the boyfriend of Stephanie ( who was Jay ) would give her a gift on her birthday, but if someone else, such as Adnan was wasn’t her boyfriend would suggest Jay ( actual boyfriend) to buy her a gift that it wasn’t a normal. Sarah might have not known about the close friendship of Adnan and Stephanie so this might had put her in surprise