The article is written with the same speculative insights as an angry manchild before breakfast, but they do correctly spot that Thomas Fischer was a contributor to Rigs of Rods, and decided to go in another direction from what he had learned there.

To call it copying is quite harsh, since he did change the engine and did write large parts of it.

It would be like calling LibreOffice "stealing" Microsoft Office, when one just served as the inspiration for the other