I generally take “content” to be media produced for distribution and consumption on online platforms, where traditional media has not already well established roles and so on. So YouTubers, twitterers, podcasters, etc. Like if you’re a musician but all your work center on releasing videos on YouTube or Vimeo then that’s now contextually made you more of a Content Creator than a musician focused on making music and releasing it in the traditional ways. For easy example Pomplamoose made YouTube videos, not just music videos. Some people show how they setup a song or make a musical thing before dropping the hard beats like Our Boy Frank Javelonious Cee-Bisquick.
So like, authors “create content” in a way, but I don’t think we consider that Content. In their role as author, creating a book, we have long defined roles for that. If there is a person who is an author then releases dedicated “content” via YouTube like Hank Green, or a podcast say, then in that capacity they are a “content Creator” for sure.
If an author formats their work into ways consumed via modern digital media distribution, then that’s clearly it too.
I have a long list of channels and sources I follow. That’s not to say they are all reliably excellent. I’ll have to think about those that are.