Its cause humans are confusing. That's why I only fuck with animals
I think the girl who said that meant to say that Yuuki is stupid thinking that Matsu-san could be different from the average elite alpha who only takes another elite as a lover. At least that's what I understood as she was talking about "normal" people and top class.
If we look back to the early chapters of the manga, Yuuki has zero confidence in himself and thinks he's not worthy of being loved. Hikari, the sweet angel, helped break the ice by wanting to be friends, which helped open up Yuuki to the rest of the family. However, there is still that underlying inferiority complex, and that silly classmate brought that inferiority to the surface, hence Yuuki is unable to believe that Matsu is actually serious about him.
Can someone explain what happened? Why did Yuuki reject him? I think I didn't understand the translation. "you think he's different for wanting a lover" and matsu san proving that he is different and not just playing with yuuki should be a good thing right?