After "she" said no, then Altman auditions a bunch of voice talent and picks someone who sounds just like SJ. I guess that's just the kind of voice he likes.
So, Altman has forgotten about SJ, has 5 voice talents in the bag, and is good to go, right? But then, 2 days(!) before the release he calls SJ again, asking her to reconsider (getting nervous about what he's about to release, perhaps?).
But still, maybe we should give Altman the benefit of the doubt, and assume he wanted SJ so badly because he had a crush on her or something?
Then on release day, Altman tweets "her", and reveals a demo not of a sober AI assistant with a voice interface, but of a cringe-inducing AI girlfriend trying to be flirty and emotional. He could have picked any of the five voices for the demo, but you know ...
But as you say, he's not admitting anything. When he tweeted "her" maybe it was because he saw the movie for the first time the night before?
According to the article, the word After here is incorrect. It states the voice actor was hired months before the first contact with SJ. They might be lying, but when they hired the voice actor seems like it would be a verifiable fact that has contracts and other documentation.
And like others, not defending OpenAI, but that timeline does tend to break the narrative you put forth in this post.
He probably just really wants to actually have SJ's voice from the film. But SJ doesn't really have a right to arbitrary west coast vocal fry female voices. Without the "disembodied voice of an AI" element, I don't think most people would note "Oh she sounds like SJ". In fact, that's what the voice actress herself has said -- she hadn't gotten compared to SJ before this.