Yeon think he knows you because even he doesn't know you follow him, he was still somehow able to feel your presence each time, because it was for a long time, that presence gave him a feeling of comfort, love, affection, and he got very attached to it. And unknowingly you. If Yeon was your lover, then he would be obsessed with your waist, would be a bit posessive over you, shower you with love and affection, baby you and so on. He would be overprotective. He has brown eyes, but it glows ember.