He has a proficiency with a rapier that doesn't come from his race or class.
He's called the Blade.
We meet him while he's training sword fighting techniques.
The "just a title" angle doesn't feel good to me.
Obviously, so many folks think his character would function better as a Hexblade for a reason. It just makes sense. Or at least him having the pact of the blade, which explains his odd proficiency. Now it's just a question of beefing up what Pact of the Blade means in BG3, because what it means in 5e probably doesn't translate that well into the game.
He can't be a hexblade, since he has a fiend patron that is important for his backstory.
And as you said, his rapier ability has nothing to do with his class, so maybe in full release he might be multiclass.
