A lot depends on how the locals use their slings. If these are peruvian shepherds, then they are going to be more target oriented than distance.
Most of us europaens tend to mainly sling for fun and distance.
How large were the missiles they were slinging ?
How long the slings ?
How old the participants ?
many of the balearic slingers would struggle to make 100m.
Because that's not their day in day out slinging aim.
A sling is a tool that has many uses and configurations.
It's all relative