TikTok uses behavior and content analysis, not social graphs.
TikTok is an algorithm-first company. Unlike Clubhouse or Facebook, it does not mainly rely on the social graph but has built a powerful recommendation engine. TikTok’s machine learning magic is a supervised learning system that finds videos interesting to the user by measuring how long you look, how fast you scroll, and many other behavioral features. Additionally, the algorithm evaluates the actual video clip: content, speed, sound, colors, words. Bytedance has an absurd proportion of their software engineers focused on their algorithms. This data has created a sizable moat that not even Facebook could cross easily.
— Clubhouse’s Future Depends On Data - How To Build A TikTok Like Algorithm · Forbes