I'm guessing that the judges switched their decision because it's only towards the end that he started acting in a way that remotely resembled the character he was cosplaying as (no, really, Artoria Pendragon would get pretty flustered over someone claiming she's the most beautiful woman ever), whereas before he was pretty much very OOC with his nervousness and gloomy reaction to being overwhelmed by the Nero cosplayer's beauty and radiant smile.