As a Guide, it is very common to see Newplayers say in the Newcomers Chat that they were randomly ported from Boralus to the entrance of the Alterac Valley battleground in the Alterac Mountains zone.
I have also personally experienced this issue a couple times and I believe this bug to happen due to some strange interaction with the Boralus boat and the phasing provided by Timewalking Campaigns.
As far as I can tell, max level characters don’t seem to be affected by this. But newer players that are still finishing their Tiragarde Sound quests are also affected by this.
Looking through old posts, we can see this is not a new issue and has been happening at least since Shadowlands’ launch:
It may seem random, but the entrance to the Alterac Valley battleground is known to be one of the default places the game ports a player when there are bugs in instance teleport (another being the Westfall graveyard).
Unfortunately for Alliance players, this place is very far from any kind of flight master and can been unbearably frustrating for a new player without mounts to reach any friendly near city.