More and more content that gets posted on Facebook, gets posted using some sort of application that will only allow access to the content if you sign up to give them access to your Facebook account.
Some, like this one, make easy for half-asleep/new users to grant access without realising it. The button doesn’t say grant access. It’s worded in such as way as to be correct in context, but to also imply that you’re just watching a video rather than signing away any privacy. From my point of view, a company that would use that kind of subtly wrong psychology is not one to be trusted with my personal information.