The statement linked, apparently quoting Johannson, states that Sam Altman himself contacted her nine months ago and requested her cooperation in using her voice.

That was declined ...

It appears they continued w/out her using a voice so close that close friends are unable to tell the two voices apart.

"Accidently" indistinguishable is not a thing.

See: https://news.ycombinator.com/item?id=40421564 for another comment that hammers that point.