Nell said:
Really as in "does it actually matter"? Not as far as I know. But it is something the player only learns if they find Ranni and join her in-group. Iji says "apologies for the deception", as in it's something the player [character] isn't intended to be in on at first. It is something revealed, ie. a spoiler for those who may value it being revealed to them in the intended fashion, rather than from sources outside the game. It is vanishingly minor as spoilers go, indeed, but nontheless against Danbooru convention for avoiding spoilers in tag names when possible.
Fextralife already reveals it to anyone that tries to look him up, as they use War Counselor Iji as the name of his page, and it's the first result if you google "iji elden ring".
And I'm gonna be frank, I really don't care about spoilers that aren't actually spoilers. "Something the player only learns if..." as a criteria for something being a spoiler makes everything a spoiler. The existence of items, NPCs, insignificant events. A real spoiler is a character death, a character being alive when they were thought to be dead, information intentionally kept from the audience so as to be a big reveal. Archer's true identity is a spoiler, its reveal is a major plotpoint to the F/SN story. Iji's real title has no bearing on anything, it does nothing to reveal his affiliations, and in game is little more than an easily overlooked change in his menu when speaking to him. If this is a spoiler, then this entire website is a spoiler.