We definitely recommend thoughtful precaution when working with third party content.
There are different types of content out there. News articles or industry events are great content sources that you can safely use. Facts, news stories, and public announcements are considered knowledge within the public domain. Reports of world news is an example where nobody owns the rights to something that's happening in the world. As as another example, if Facebook announces a new feature, it's a public announcement and the content of the announcement is not proprietary.
We do not recommend using someone's hand-crafted opinion-based writing or research findings, at least not without explicitly crediting the author. Lumen5 gives you a lot of flexibility to edit your content, so you can add your own commentary, apply your own angle, and like other forms of art, using something as inspiration is fine as long as you're introducing new value to the narrative while crediting the source where necessary.