They are born of the same stock and have the same goal in mind, but the main difference is this: with content marketing the brand becomes the publisher.
Exquisite examples of content marketers:
Red Bull
GE
Mint
Magnolia
In each case the brand creates content that informs, educates, or entertains. It's how you build an audience that builds your business.
Native advertising, therefore, is paid content that drives traffic to that content.
And for a final comparison, guest posting is non-paid content that drives traffic to the content on your domain.
There you have it! An introduction to native advertising that helps distinguish it from other types of advertising.