Depends where they were going to load and where they were in turn taking the loaded train. Sometimes it is easier to have a loco & crew either end to reduce the time spent reversing direction.
If you caught up to them at Cunningar, there is no possibility of the locos running around the train as it is a single-ended siding with a single crossover. They probably would have propelled into the siding, loaded, come out onto the Up Main north of the crossover, then handed control to the crew on the southern end for the return to Harden or Coota, operating under their directions power-wise as required.
We regularly did this on the Vales Point-Teraba jobs, to avoid securing the train at Sulphide. Pull in, cut out the brakes, a quick leakage & continuity test by the crew at the other end, and depart southwards again.