You're the one who doesn't know what it means. Yusuke was never intended to be a demon until this shit was pulled out of the author's ass at the last minute without literally any foreshadowing or build-up, and just because the author came up with a bullshit explanation for it to work in-universe doesn't stop it from being a retcon. He was just supposed to be a regular human like Kuwabara at first. You alter a character's backgrounds with shit that you never intended before, and you got yourself a retcon.
You just explained why you're wrong. Good work. A retcon is something like Cory and Topanga being together since they were babies when we literally see them first couple up in 5th grade. It changes established lore. Yusuke having demon ancestry doesn't change a damn thing. It doesn't contradict anything. People get butthurt over the simplest of things when it comes to their precious animu. ---