So it obviously would start in a very broad content but already target at my demographics (male 30-40 y/o, which BTW gave a worrying amount of very young girls dancing in a sexualized way) but with time it would certainly adapt and be really spot on on the videos I liked (mainly stand up/comedy stuff). Everything based in signals other than liking of following.
They obviously track all interactions from the user (time watching, repeats, shares, OP profile checks, etc) to make this targeting. Also its ML for visual recognition used to identify key aspects on the video (people, location, etc...) is very powerful as it would guess my favorite comedians and start exploring with other videos.
Also they certainly use bandit/lookalike model there as it would recommend some wildly different videos for me.
And I can bet that that last video it shows when you click to leave the app (on Android at least) is probably the highest rated recommendation for you. To really lock you in there.