The City statement was put out immediately after Gerard's comments (prematurely). The complaint was never progressed by the keeper and there was not enough evidence. So it never was an assault. At worst it was an allegation. As far as I know the BBC have never corrected their original story or made any attempt to check the story.
I don't think the whole BBC is biased. But I know for a fact that some individuals within the BBC Online football operation are biased against City and seem incapable of reporting on the club in a professional way.
The City statement was put out after everyone saw what happened and the club chose to call it an assault because it was, accidental or otherwise.