I do not have any idea, why they served chicken mu when I ordered Chicken at Chicken restaurant.
We usually eat chicken mu together when we eat chickens such as Chicken(KoreanFried Chicken), Yangnyeom Chicken (Fried Chicken but coated with spicy and sweet sauce), Barbecue Chicken, Ganjang Chicken (Fried Chicken but coated with soy based sauce), Jeongigui Tongdak (Whole Chicken roasted over an electric oven)…
So, Chicken mu is a just side dish for Chicken.
These day, Spicy food is gaining popularity in Korea, Spicy food means not spicy but really hot and spicy like a Dakbal(Chicken Feet coated spicy sauce) or Spicy taste of Tteobokki.
When we eat spicy food, almost restaurant served Chicken mu.
Sometime Chicken mu does save me from spicy tastes.
If you visit South Korea, you will have chanced to eat Korean fried Chicken or another kind of chicken. when you eat chicken, you will meet chicken mu.