Pretty much, the three terms are interchangeable in many cases. I’ve done content writing, content marketing, and copywriting before depending on the situation. I don’t worry about the semantics much.
All i care about doing is helping a business getting more leads and sales, which is what all three of these terms refer to. though I do tend to be most into the idea of content marketing because it ties very closely to SEO, which is also what I do for clients.