Two incidents that come to mind with regard to non-riders asking questions or commenting on the bike have to do with the mechanics of my old F650GS. As I pulled up to a stop one day I noticed a long metal pole just to the left of the bike so I kicked it out of the road so nobody else would find it the hard way. The bus driver next to me slid open her window and said "Sir! Sir! I think your kickstand just fell off." I thanked her for her concern and explained it was just a metal rod in the road. Another time a gentleman approached me at a gas station to show me something was falling off my bike. It was just the Scott Oiler dispenser reaching down towards the chain at the rear sprocket. I explained to him what it was and he was intrigued that such a thing existed.
As silly as the questions/comments may seem, in these cases, I'd much rather people ask me about potential problems with the bike than to say nothing when they see my wheel falling off!