It hurts seeing Mooyi accusing Youngsoo like that, but the detective suggested that it could be a possibility. I mean, even the slightest possibility... no matter how nice and good a person is... you never know their true character and motivations. At this point anyone of Mooyi's friends can be slightly suspicious as well for the whole stalking thing (I still don't trust this green-haired chick, lol) for any kind of reason.
I insist that the chef is still suspicious about the whole ordeal, too. Even if his "participation" could be mostly surface-seen. I still don't think it has been explained why he has some kind of interest in Mooyi despite all the closeness they have been going through in that one reality show they are still recording. I would understand him helping Youngsoo out of good faith... but he is NOT that close-close-friendly with Mooyi, yet, despite everything?