They might have something, at that time carmack was an employee of Zenimax, there is a strong argument for suggesting anything you do on company time on their hardware etc is owned by the company.
Carmack has gotten into trouble over software patents before with Creative and the OPENAL stuff via Doom 3. Hence why you realistically needed creative openAL sound card for quake 4.
They are obviously hoping because there is so much money involved zuckerburg will throw them a bone to keep them happy if they can make half a case.
With the right amount of money and legal team you can make anyone else's life difficult. Especially in the good old US of A.
For the sake for a few hundred k in legal fee's, Zenimax probably think its worth testing the waters. From a purely financial POV they are probably right.