Running to standstill

I guess I understand talking to someone while they're jogging. Today while I was pad-padding around a local woman smiled and said "You're doing well", a local man said "Work harder", a couple of elderly sisters on holiday clapped. All you have to do is smile good-naturedly and keep going.

What I don't get is actually stopping a jogger - isn't that like calling out numbers at random when someone's trying to count? It's happened a few times now (all Germans actually, but I'm not sure that's relevant). I stop because I presume they're lost or have something urgent/vaguely important to ask. But no, they're just curious about how long the perimeter of the car park is, in metres.

Do I look like I'm rolling a circle?