Earlier quoted context omitted.
It's not just made up, it tracks downvotes from extension users and combines them with a historical database. And I think some creators share new info with the database to help the accuracy.
Creators can only share own counts and would be heavily incentivized to lower their dislike count, no? How is this supposed to work?
New videos will only show dislikes sent by people using the extension. There's no way to know the real number anymore.