Why did Hitomi say aiya in episode 5?

She said it a couple times. Another character laughed and said something like "What are you, Chinese?". I didn't hear her saying it in any other episodes. I think the only other character(s) I've heard saying aiya were a Chinese monk Mao fought. My theory was that Hitomi might have learned aiya from the owners of the Chinese restaurant, but I wasn't 100% sure if it was near the bar where she worked, or if that was another Chinese restaurant.