Extracurriculars are of course relevant, not just for the scholarship. Every interview asked this question and the schools want kids who have a balanced lifestyle (and still achieve the exam score for that school) so they have the "capacity" to increase learning time later on, I suppose.
For St Paul 11+ (boys), the interview is for 3 hours and comprises a one-hour session in which each boy has to choose an activity (art, drama, music, or sport). Maybe they are not evaluating their levels, but certainly, want a boy who is committed and passionate about something outside academics.