The so-called "wearing a horse's pelt" means concealing the Qilin's true immortal form using divine arts so that when other great spirits scan it with their spiritual sense, they can only perceive the illusion of a horse.
In the Classic of Mountains and Seas Realm, the Qilin and Phoenix clans held a status equivalent to royalty and nobility in the mortal world, which would easily draw unwanted attention.
The Qilin had tailed them the whole way, originally intending not to disturb Xu Ruoping and Hu Yihui, but it was accidentally discovered by a Tulou beast along the path, which surrounded it and continuously spewed poisonous mist in an attempt to devour it.
Chapter 243