NOTE: "Theoretically" hackable because everything is on the same CAN bus aka network.
They did not hack anything.
I do agree that the control systems should be isolated from the rest of the unrelated electronics as a matter of good canononical security architecture.
But if they added appropriate layers of security to the systems despite the shared bus then the Jeep is fine. I still personally prefer as many layers of security as feasible including network isolation though.
But I will be seriously enraged and immediately dump the Jeep and the Chrysler brand forever if I ever discover that there is a remote vulnerability. There is no f*cking excuse for that sh*t when it comes to a motorized vehicle. I don't care what the R&D costs are.