Bloodknights are interesting, and its an interesting portrayal how they have done them. It shows that there is in fact multiple ways for them to come about. This is how vampirism works as well. In Tes, vampires are portrayed as multi origin while lycanthropes are singular origin, this means while there might be a few or several that have Molag Bal as the creator there is many bloodlines that Molag Bal likely never created or even had a hands in.

Molag Bal isn't responsible for all of them and this is how the lore is portrayed on the matter even one npc disputes the entire idea of Molag Bal being the creator. Lore wise, magical items and the curse of a wizard can do it. Necromancy is believed to be what creates vampires along with false gods in Morrowind. Alchemy is a confirmed way for vampires to come about. So Magic items, curses, necromnacy, alchemy, and Daedric means, Maybe even some being aedric are all ways vampires can come to be. As the Dunmer consider Aedra to be false gods.

With Bloodknights while alchemy can create them, a cannibalistic vampire that feeds on multiple strains can become one. Chaotica creatia from Coldharbour isn't needed as the stuff used in the Stone garden Dungeon is another way of doing it. So there is multiple ways to create something and this is how it is in Tes. So there is three ways known ways Bloodknights can be created.

What most people might not understand is they don't run off anything being definite. This way they can do many stories even if they are conflicting with other stories this is in fact how Zenimax operatives as its been stated by devs. What npc people believe in the reality is what sets the lore. So for example Molag Bal created several bloodlines of vampire but people believe this or state it and that makes it true.

But there is others that will belief they were created by necromancy, others by curses. Some maybe by a different prince all together. So in that way all those origins would be equally true because Bethesda made it so all the lore comes from the opinions and beliefs of mortals. Its the npcs that make the reality the way it is and everything about it comes from that prospective.