Percy singing and smirking in the pub totally different from the person he is compared to how he is in the school (canon). As he have muscle and tattoos and piercings and hair colour changing charm and relaxed and confidence and sex appeals as In the school he is very awkward and not confidence and uptight and strict about rules. When Bill, Charlie, Fred and George walked in the pub which is a new place for them and saw Percy singing and they are in disbelief and confusion as they only saw how he was in school. And they are talking about how confused they were and how he is able to show his sex appeal when singing but unable at school?