I'm not sure why those things would discredit it. A leak could be bits and pieces compiled from separate sources. Some of it could be copy-pasted from official overview, some of it could be added in from memory.
Avaloren is the spelling that we're familiar with from an ancient document written by a Watcher. That doesn't have to be the exact same name or spelling that the locals or others give to it.
The part about the leak that seems credible to me is how it would appeal to new players. It's a fresh continent, with a different history. The game is 20 years old, and it needs to appeal to a literally new generation of players to survive.
At the same time, it tries to keep the current player base happy by branching off of established but unvisited lore about the emergence of Night Elves from Trolls. It offers up exploration of the nature of Elune. It offers a personalizable spot in the world that won't be as isolated as previous iterations. It offers the ability to customize the appearance and feel of class abilities without changing their mechanics. More personalization and ownership keeps people invested, even if it's largely cosmetic.