There are obvious differences in meaning and origin between "mundane" and "red dust".
1. Meaning. The mortal world refers to the human world, that is, the secular world, while the red dust refers to the flying dust in the busy city, which is used to refer to prosperous places.
2. Source. Mortal dust comes from the second chapter of "Liu Xingshou" by Yang Jingxian of the Yuan Dynasty: "Follow me to escape from the mortal world and become noble." The origin of Hongchen is earlier, mentioned in the Eastern Han Taoist work "Dongzhen Taishang Ba Su Zhen Jing": "Escape from the world of mortals and escape reincarnation forever."
In general, mortal world and mortal world have obvious differences in meaning and origin.