The welder terminal voltage would be about 1.4 V + total lead voltage drop. There are two types of welder supplies constant current and constant voltage. A constant current type would be selected for this type of tester. They behave much as any other CC source but the slope on it is only accurate enough to meet welding requirements.

I thought that 1480 millivolts would still be millivolts :)

The internal connection s to the bars will probably include more than one coil set. This is done to reduce transition arcing and make operation smoother.
The rewind shops around here test windings for shorts with a machine called a growler. The name tells all it is an electromagnet with the pole pieces faced to a v. The device under test is inserted. Proper windings just hum while shorted windings growl because the shorted turns use power. I would assume that by the time the rotor gets this far it would have been through a growler test.
This seems more of a quality control test for the correct number of turns present in each coil than a shorted turns test
Terry