When Lachlan sees the other boy lift his cup, his initial thought is that he's saying a long-distance hello to...someone that's not him. He doesn't know who anyone is apart from Addy, after all, and nobody should know who he is either. But there's no one behind him. Maybe he's worse at this anonymity stuff than he thought. Or maybe the other guy is just being friendly. He smiles hesitantly and then walks over even more hesitantly. "...Hey. Enjoying the party?"