tl;dr: The browser attempts to learn your preference for each site automatically based on how you interact with videos. You can see what it's calculated by visiting chrome://media-engagement
Oh god, that reminds me of another piece of bullshit Chrome magic. They made a system when the browser shares signatures of forms/fields with a central server, which sends back "crowdsourced" autocompletion rules, and they've made it almost impossible for developers to stop it from doing that [0] even when it's flat-out wrong and users are complaining about inappropriate autocomplete suggestions being shown/recorded.
Over the last ~8 years developers have submitted hundreds of examples [1] of why it's a stupid feature that at least needs a way to opt-out, but Chromium devs have kept it mandatory, and I suspect it's because Google/Alphabet is somehow exploiting all that leaked metadata about what forms people visit.
P.S.: Messing with the issue-tracker (and bringing up unpleasant memories of desperately trying to find a workaround in their source-code) I find that the two linked issue about this anti-feature rank are both in the top-15 most-voted open issues. (Rank 14 and 9, respectively.)
tl;dr: The browser attempts to learn your preference for each site automatically based on how you interact with videos. You can see what it's calculated by visiting chrome://media-engagement