I think part of it is that the Warrior of Light being a primal has been a (incorrect) theory for a while on the English-speaking side of things. So seeing that fandom theory being used as a joke in-game is funny. Even more so from Y'shtola who isn't known for having a sense of humor.

That said... Localization and Translation aren't the same thing. And it's not like any plot-relevant information is being lost here by changing it. If was like... something to do with how souls worked and how the Scions are getting home, then that'd be bad. But it's not.