It is also a brand new timeline/universe that exists on its own. It didn't displace or change any other timeline. Nothing is "wrong" or out of place because of its existence.
We've seen such new timelines more than once in Trek, and the original timeline could always be (more or less) restored.
If Spock could contact Picard in the Prime Universe and told him about Nero and what he is about to do, then Nero could be stopped from going back in time ... and the nuTimeline would cease to exist. The perfect Reset Button!