If there really are concept art in the game files that indicate the difference, then perhaps everything happened this way:
1. Dom K'Vash created the Sirius Nomads, who are hibernating/learning/doing whatever they were doing before the human colonization began.
2. Dom K'Vash created another, less intellectually-blessed race of Nomads which has only one goal - that of protecting Sirius from outside threats. It's only natural to think that the guardians possessed better weaponry thus explaining why the Sirius Nomads didn't pop up systems.
3. The Nomad Guards had their attention drawn by the everlasting Alliance-Coalition war and decided to eliminate the threat. It was only a lucky coincidence that the sleeper ships were sent to Sirius shortly before Sol blew up.
This is just a hypothesis.
@Sead -- before I read it, can you tell me who wrote it and if it is officially considered as lore in Discovery?