Final answer:
Jeff's teacher was surprised because, in French culture, teenagers are expected to use formal greetings with adults to show respect.
Step-by-step explanation:
Jeff's teacher was surprised by his friendly greeting because French teenagers usually use a more formal greeting with adults. In French culture, it is customary to show respect to teachers by using formal titles and language, such as "Bonjour, monsieur" or "Bonjour, madame," rather than informal greetings like "salute." This cultural norm emphasizes the importance of propriety and respect within the educational setting, which contrasts with the more informal approach often observed in American culture.