This is a unique network structure. It’s a new way of determining who should see what. It solves a problem (pressure-free photo sharing within specific contexts), and because it’s a network rather than a format, it’s going to be hard for Facebook to copy.
Facebook, Instagram, and Twitter all build their feeds from content shared by friends and followers. The pool of content their algorithms choose from is limited or scoped. TikTok’s feed however is built from content shared by any user, regardless if you know them or not.