I dont really think Halsin was even once adressed, called, or even mentioned as Archdruid ... Unless i forgot something, all NPCs i recall called him "first druid" ...
Same thing. They use the titles interchangably. Mouse over Kagha and it'll say "Archdruid" under her name for instance. But if you need a direct mention:
Originally Posted by Nettie
Not me, my mentor the archdruid Halsin
Agreed, either, they use that title wrong or Halsin has somehow lost power.
As for the werebear theory: I would like it, because then his sudden changes make sense, but that would mean, there is no chance for Helia at all anymore.
Honestly he seems way too low level a character to be arch anything. In 5e to become an archdruid you must be a level 20 druid and have a wisdom of 20. So the title definitely seems badly misused. Hopefully this has been fixed for the full release of the game.