Eredar Voidcallers

I don't understand the lore of the Eredar using void magic. In one of the Broken Shore world quests there are "Eredar Voidcallers" using summoning magic to bring forth "Shackled Voidlords" that you have to fight.

I know Sargeras isn't one to shy away from using the weapons of his enemies (see: the entire Burning Legion) but it seems a stretch that he'd allow his followers to use void magic and even go so far as to summon Void Lords (even shackled ones) to Azeroth, when his biggest fear is the Void fully corrupting Azeroth's world soul.

These don't appear the be the Voidwalkers that were retconned into being Demons instead of servants of the Void Lords, they have a different model and Velen talks about them specifically of being part of the Void during the quest.

Does anyone have an explanation for this? It seems so strange to me.