Seriously?

Just today, most of our teachers are keep on mentioning that our class is really different from others. They keep on telling us that our class is very serious. We do not laugh on their jokes, we are not joking and yeah we are just really serious. One of our teacher said, “I do not know how to teach this group of students.” (non verbatim). Then I have these questions in mind, “Why? What is wrong with us? What is wrong with being serious?”