The thing is the case isn't that simple, Zenimax has presented no evidense that even a single line of code in the Rift SDK is theres. Instead Zenimax's entire case revolves around the fact that John Carmack was helping Palmer Luckey with the Rift as a personal side project, Zenimax is claiming they own any and all code written/co-written/or consulted on by Carmack or any other Zenimax employee, even if said code writing/consulting was done on the employee's personal time.
In others words, the entire suit is purely dick move by Zenimax.