That's far from true. They have world class expertise in design and supply chain management. That would transfer over to the car market a lot easier than it would to pretty much any other trillion dollar market.
Shipping a billion iPhones and shipping millions of cars only reasonable each other at a surface level. Apple does not have much expertise in maintaining the same supply chain and logistics, and certainly not in design.
They could hire people with the expertise, but Apple is allergic to growing engineering expertise outside of Cupertino.
I doubt that's Magna Steyr's fault though. They've produced 10k cars, but Fisker have only delivered half of those, and from everything I've seen, it seems to be well-built from a hardware standpoint.