HAtton uses blue moon because it is Manchester City's hymn (well, as almost every football clubs in England, they chose an existing song as their Hymn) and City is HAtton's favorite club because, among other things, his father played for that team, hence why he also has light blue color on his trunks and entrance robes. PErsonally, I do not consider he ripped that song out of nobody's clenches, it is just an emotive and kind of tradition song considering his "footballistic" and family allegiances if we can say so.