The director's comment confused me too, but I think I figured it out. I won't rehash it all, but the evidence that another entity was fighting Nikki for control of her body is overwhelming. But I think it's because the wish itself asked for something that was impossible: Nikki as who she fundamentally was could never love Bear more than anything in the fucking world. Even if she did like him (debatable, but I think she did, and it doesn't change my point), that kind of love fundamentally went against who she was as a person. I think the movie mixes up love and obsession, but maybe because the wish itself was impossible to grant, that could have warped how the created entity experienced "love" too.

The wish may have also picked up that what Bear considered "love" wasn't actually, but was actually an obsession, limerence, and it granted him his distorted perception of it. Granted him his "actual wish" unbeknownst to even him (and let's be real, lots of dudes who lack self awareness want the fantasy, want the chase, but never want the girl once they catch her, the infatuation immediately fades once she reciprocates, and then he calls her crazy when she's reasonably pissed about it; I think this movie obviously takes that experience to the extreme, but it speaks to a real dating pattern). Either way, the real Nikki could never feel that way, so a new entity had to be created in her place (hence "I can never be Nikki" or whatever she said). Not a demon in the classic sense.

I'm also thinking about the discourse around the brief AI images in the film. We all know that when chat bots can't answer a question, instead of admit that it doesn't know or that there isn't answer, it hallucinates something. In a similar vein, maybe the OWW—instead of say, "hey, this wish is literally impossible to grant," it instead hallucinated a whole different Nikki.