The article skips a lot of context to make it sound significantly worse than reality. Facebook didn't just randomly give Netflix access to everyone's messages. Specific user would need to purposefully log in to the Netflix app with their Facebook account in order to grant Netflix access to the chat functionality (intended to send movie recommendations to Facebook friends inside the Netflix app).
https://about.fb.com/news/2018/12/facebooks-messaging-partne...
Disclaimer: I work at Facebook but not on messaging or anything related to this article.