Facebook has an ingrained formula that monitors how you interact with your friends and then kinds appropriately. Source
Facebook Mobile Friends List Order
While the precise ranking algorithm is secret, it does take into consideration the following factors:
* How usually you visit your friends' accounts
* Just how typically you click on your friends' web links
* Photos/tags in common
* Typical teams/ organizations
* utual Friends
* How commonly you look for friends
* Loved one appeal (how preferred your friends are amongst your shared connections).
So, the actual sorting is not random, however instead meticulously crafted to facilitate communication as well as site interactions.
