You're forgetting the tax credits on the Model 3, which probably won't exist when the Model Y is released. This is also an important factor for the future because the price of the Model 3 will likely be lowered as the credits expire.
It is misleading because it is a very specific case in California/US. For people in other countries these things don't apply. We have 10k euro discount to Electric cars for instance. It would apply to both cars equally.
