The article is a little fuzzy with technicalities, though it does acknowledge that this is not inherently a clear cut matter.
First of all, there is the question of copyright vs. the question of, for lack of a better term, tackiness. Was the person's work copyrighted? That's the beginning of the inquiry, not the end. If so, then what are the unique attributes that are being claimed? Do they arise from the script? (If so, you're likely dead in the water.) What has the person done that is actually original (being mindful that it is a natural human trait to think we have invested things that already exist)? When one studies history (theatre or otherwise) one tends to discover that there are few new things under the sun.
Secondly, there is the circumstance of people in uneven bargaining and financial positions. Settling a case does not always equate with being wrong.
All of this said, there are of course people who steal intellectual property just as there are people who steal tangible property. My feeling in general is that an auteur director is more likely to have a claim than some community theatre director who just applied a few quick gimmicks that they may or may not think they thought up.
It's totally reasonable to be peeved when seeing these things, and I wish I had a better sense of where the author of the linked article fits into the above.