Did Milo somehow get proficiency in Elven Thinblade and Unarmed Strike from somewhere, or have all his attacks been at -4 since he got rid of his quarterstaff? Wouldn't he be vastly better off with a dagger?

He had a whole host of feats on an Amulet of Mirror Move (an obscure spell that lets you copy feats you see someone else use, which he grabbed via casting Heroism on Mordy) which he lost at the end of HPCC. This included Elven Thinblade Proficiency, because he could.