Although the 5 pin is the standard DMX connector, lots of lower end stuff uses 3pin for DMX. Pins 1-3 are wired exactly the same for 5 and 3 pin. If the person had the skill to swap connectors, they probably knew to swap them 1 for 1. As an experiment, you could swap the wires on pins 2 and 3 and see if that made any difference to your dimmer pack; it won't hurt anything. Are you sure your dimmer pack takes DMX and not 3pin Microplex/LMX?