"Corley denied the motion, and in doing so, set the precedent that licenses like the GNU GPL can be treated like legal contracts, and developers can legitimately sue when those contracts are breached."
The GNU GPL was written on the basis that if someone does not accept its terms, then that without any other license from the copyright holder, redistribution puts that person in violation of copyright law.
Suing for damages on the basis of a breach of copyright law clearly does not require any contract.
So this is more about a technicality of the legal process in this particular case, rather than anything about whether copyleft is legally enforceable or not in general.
Specifically, because the motion denial was based on the defendant's own admission being deemed to be the agreement of a contract, this says nothing about the general enforceability of the GPL (future defendants could simply avoid making such an admission).
Further, since the ruling was in response to a specific motion, it only concerns the claims made in that motion: about whether a contract exists in this particular case. It says nothing about the "copyright violation if you don't accept the license" mechanism of copyleft.
Finally, the article does not provide any evidence that there has been any ruling that determined that the GPL is an enforceable legal contract, contrary to its title. The ruling as quoted just says that the defendant, by its own admission, did accept to enter in to the GPL-defined contract.