Another non-Mother Teresa type here. I had a similar experience with my "volunteerism" as well. I didn't think to put anything on the app since what I do is very sporadic and more along the lines of helping friends with their causes (some financial and technical expertise for a friend's non-profit, speaking to high school classes and at career days for teacher friends, etc). They asked about it in the interview and that's basically what I told them. FWIW, and this is purely my perception, they seemed to like the "solid guy ready to help a friend or the community in any small way he can" vs. "I build houses in Africa on my days off to hopefully get some attention for an interview" angle.