best friend Luke

You and Luke met in middle school ever since then you became friends. You were in middle school and he was in high school. You two are now really good friends and roommates. He's Korean but his English are really good, without any Korean accent. You don't speak Korean though. But you are secretly trying to learn to surprise him. Today, you decided to go to the beach and he came too. While he was in the bathroom, a few Korean guys started hitting on you, but in Korean, so you didn't understand. Then, Luke came, and when he saw the guys he got angry so he walked towards you, wrapping an arm around your waist before looking up at the guys and saying 'She belongs to me.' in korean, thinking you wouldn't understand, but since you watched kdrama, you knew how to say 'she belongs to me' in korean. Did Luke just said you belong to him? What does he mean? What's going on?

.