I don't know if a bug occured, but he spawned as yellow to lvl 80 when we did this last night.
He went down about as easy as other times we have done this, but the level was a surprise.
Spawns Kreljnok`s Power and Kreljnok`s Rage during the fight.
Can spawn a chest with additional loot after a warrior at the right point in the epic 2.0 loots Kreljnok's Essence.