Excuse my ignorance, but why does Nale hate Malack?

[FujinAkari]

Ah, the "some person I won't name or give a source for says so" argument. Well here's two sources that say it only dates back to 1973, and always meant changing established continuity.

Retcon is a shortened form of retroactive continuity, and refers to a literary device in which the form or content of a previously established narrative is changed .... The term appears to have its roots in a 1973 book by E. Frank Tupper titled The Theology of Wolfhart Pannenberg: “Pannenberg’s conception of retroactive continuity ultimately means that history flows fundamentally from the future into the past.”

and

Retcon is a relatively new word that was first included in the Oxford English Dictionary in 2012.

Do you have a source for the word existing in a different form prior to that?

In addition to this (and I apologize if it feels like I'm piling on,) would it even matter if the claim of a different historical meaning was true? If the argument is "Oh, well there is this other definition that is now obsolete." If the word is accepted to mean one thing, then that is how everyone will use it. Unless the poster is as vampiric as Malack, there is no viable reason for the outdated usage to be used. :)