Not sure how you reach that conclusion. One factory (Fremont) on West coast making cars for West coast, one factory in the middle of the country making them for the East coast. Makes perfect sense, cuts down on transportation costs and time.that could be the safe interpretation that it is one factory in Central USA.
However, it is weird to say that Y production is only for the East Coast so i still think he's talking about two factories.
My vote for Tweet interpretation, one factory, two production lines.