My guess is that Zenimax wants to get access to the source to go on a fishing expedition.
He's friendly and is exactly the sort of engineer that helps teach others how to do things--just look at the GPL releases of all the old Quake stuff when it came out (back in the 90s!).
Back in the day id programmers shared snippets of code with whoever they wanted - they didn't need to ask any corporate overseer for permission. There were a few little bits found when the GarageGames/Tribes engine code was first released, for example. (pretty sure they got those lines of code from Brian Hook, but it's been a long time...)
Still, the point stands that this isn't unprecedented. John Carmack's has, in the past, just helped out potential competitors before.
That's the key word, isn't it.
If the Oculus guys weren't absolutely clear about who owned what, and what the patents were, then they're screwed.
By which I mean, they will for sure be embroiled in a long and costly legal battle, unless they settle.
But:
> ZeniMax provided necessary VR technology and other valuable assistance to Palmer Luckey and other Oculus employees in 2012 and 2013 to make the Oculus Rift a viable VR product, superior to other VR market offerings.
My guess: it sounds like John Carmack began an informal relationship with Luckey and Oculus, and possibly wrote some code for or advised them while he was still at iD. If so, Zenimax is likely legally in the right. Yikes.