SEO is technical subject matter for every website which want to rank organically.
Content marketing is the more to do with promotion of website both organically and paid.
Content market compliment SEO process. Digital Marketer use the key words which help rank website for content marketing and using the keywords use the content in different social media channels. This would help in better promotion of the website over time. It need not be paid.
Blog, Facebook picture content, Infographic , Video are all content marketing tool. Now snapchat. Content is democratize by social media and social media platforms in true sense. Anyone can create content to promote her/his thoughts to public. Brands create content to engage customers on social media, print media and television through advertisements.
In conclusion Content Marketing help in SEO the same way SEO help build good , smart content. We should not ignore either of them.
SEO is key word dependent and key word is a content!