Exactly, the bulletin was clean and that's all that those working on it will care about. They won't be sitting there fretting because they've one version of the news theme music and not another. Whoever's on sound just cued up the clip labelled 'end sting' because that's what the needed
Of course viewers will notice and care if it's a disaster of a bulletin, but not because of a subtle athestic difference like a slightly different version of the theme tune
Some people are built to detect subtle changes in things so some viewers and potentially some staff picked up on it. It's possible that as it seems the bulletin was last minute, someone could simply have pressed the wrong button on the mixer and put that out instead of a 'generic' theme. It's easy to do, I'm not an expert but I have had experience of that kind of thing. I'm not saying that is what it is but is merely a possibility.
Theme music aside, I think it's useful having a network bulletin from Salford. It's possible that Salford could be used as a News Channel backup, as I have said on here before, without having to use Millbank. If there is a way in Salford to get things on air without the need for a gallery in London then it could be a valuable tool in case of a major issue in NBH and give them a viable full studio alternative to Millbank. As the sport presenters are present and have doubled up in the past as newsreaders, they could run the channel for a bit at least. It's certainly a good experiment which seems to have worked.