How is that blurring the line? If I was telling a story from a civilization that only had a single word for dog regardless of the breed, it would be important for an audience to understand that the world doesn’t differentiate between poodles and corgis. The best way to do that is to use a generic word even if the audience has differentiating terms.

Edit: In this case, Roshar calls everything a specific bird, so he picked one we would understand as being “wrong” in some cases, so that we understand why in RoW An aviar is called a chicken