If you're going to get technical, companion is the correct word because even though friendship is implied in its use, companions don't have to be friends, they just have to spend a lot of time together or be travelling together, which fits the bill here. Also companion doesn't imply hierarchy, it's a neutral term in that sense. And furthermore the word companion is used because it's common shorthand in RPGs for characters that form members of your party in a game.
And you're right that we don't know anything for sure, but I do think the speculation we're engaging in now is reasonable based on the information we currently have. I.E, I don't think it's unreaosnable to make the assumptions we have based on the information we have, and the information we currently have is enough to serve as a justifiable base. And by information I don't just mean that statement but also Larian's past approach to handling companions.
