Yep. There were 2 questlines datamined that could be the pre expansion "event". The horde one is something about investigating some incident somewhere about a missing team which leads up to retrieving some magic item that is used to create something special that will be used in the scenario (if you read the new WoW book or the spoilers you know what the questline is about). The Allince version of it is more or less about the same thing just with another focus like "why are there Horde boats in Darkshore?" or "why is there so much Horde activity" and so on (again some of it is mentioned in the book) which leads up to the scenario.
By saying that it's a world event and not a world event I think they just mean that you can do the questline as a world event which leads up to the scenario which leads up to going to Pandaria and that after the release of MoP you can only do the scenario.