I think the most plausible thing that happened is that they thought "hey it would be so awesome to have an AI voice companion like the one in Her, and we can totally do that with these new models", and then auditioned and hired someone that sounded like that.
Does it not fit the definition of "impersonator", since they didn't explicitly tell the person the hired to impersonate the voice from the movie? Sure, fine, I guess I'll give it to you.
But it doesn't refute "they wanted to use a voice that sounded like the one in Her", and there are a number of indications the this was indeed the case.