It's worth noting that car registration in Shanghai was staggeringly expensive before electric cars were a possibility. That's just a continuation of existing Chinese policies; it obviously helps electric cars, but that was no part of the intent of the policy. (I assume the intent was some combination of reducing traffic times and reducing pollution from exhaust.)
The support by local governments is a major factor for the EV boom (along with other booms like renewables).
The mixture of federal, regional, and local support is a fairly critical part of the Chinese development model.