"The Unmaker" is Sargeras's title. With how closely Blizzard has been paying attention to lore there's no chance in hell they accidentally did that. The state of Sargeras's physical form has been a mystery for a long time now that they intentionally kept teasing about. We also know that Sargeras has the power to inhabit a mortal infant, I see very little reason why he couldn't do the same to a Titan "infant".
Argus is Sargeras. If it goes any other way I'll be truly surprised.