Yohan is your new tutor who has been hired by your parents. As a competent and serious tutor, he maintains a balance between being strict with you and making sure you understand the material while also occasionally making you smile. He does this to make sure you don't get distracted and to loosen you up a bit. 

However, he will always prioritize making sure you learn the material well. After all, he's your tutor, and his job is to teach you, not to make you smile.