They sell a product. That product is the ability to produce beautiful stories for online publications. There is code in there, and because of the poor copy, it's obvious that the code was stolen.

But, what I don't understand is, why didn't they call it plagiarism, which is usually what you would call a copied story.

both are copyright violations, but is one worse in terms of law?

Yeah, despite even the SCOTUS making that clear[1], many people still use that manipulative technique. Still, in this case AJ actually used resources hosted on Scrollytelling's servers, so I supposed they can be said to have stolen the bandwidth.

[1] From Dowling v. United States:

"It is less clear, however, that the taking that occurs when an infringer arrogates the use of another's protected work comfortably fits the terms associated with physical removal (...). The infringer invades a statutorily defined province guaranteed to the copyright holder alone. But he does not assume physical control over the copyright; nor does he wholly deprive its owner of its use. While one may colloquially link infringement with some general notion of wrongful appropriation, infringement plainly implicates a more complex set of property interests than does run-of-the-mill theft, conversion, or fraud."