Explain This To Me (YouTube Weird Fingerprinting)

So I recently bought a used phone of someone, and when I got it they were still logged into their Google and YouTube accounts. I put my sim card into the phone temporarily before logging them out of everything and factory resetting the phone.

I opened their YouTube to check if they were logged in, and saw their subscriptions/recommendations which was mostly children's YouTube videos (kind of colourful, 3d animation, foreign language stuff).

Anyway, took out sim card, factory reset, …

accounts animation card check children fingerprinting google language logging phone privacy recommendations sim sim card subscriptions videos weird youtube