Chairboy,
It was likely that the jumpers were using an established jump zone by or at an airport. As such the aircaft in the area are instructed to avoid flying through the jump zone even though it would normally be an area they would use to get to the pattern or just to overfly the field. FWIW an aircraft is supposed to avoid a jump zone and they are listed on sectional maps for that purpose. If that field had unicom, jump operations and the area to avoid flying into would have been announced even if there is no tower.