If Tesla was expecting 50% annualized growth, or even growth comparable to their recent historical trends, they would not have cut the price tag on every model of car they sell.
I don't follow your logic here. With the reduced tax incentive, Teslas have seen an effective increase of ~$1,750 USD.
Would you normally argue that a yearly price increase of ~3% on a car portends anything in particular about demand? I guess it implies that they expected demand to fall if the increase had been ~6% instead, but that doesn't seem like anything that would preclude 50% worldwide growth.
I think you might need to brush up on your understanding of demand elasticity curves.
Tesla is dropping the sticker price of their vehicles because they think that demand for their cars is at least somewhat elastic with respect to sticker price, and they're in a better position than you or me to have the data and analysis on this. (Tesla has also announced that this is why they're dropping the price so I'm not sure why you're arguing this point?)
Economies of scale are not related to this drop in price. Economies of scale refers to it being cheaper to product an product at scale due to efficiencies in the use of the largely fixed-cost capital expenditures. Companies don't usually drop prices due to EOS until at least a quarter or two after they've reached that point in the production cost cycle, largely to confirm that they've actually reached EOS operationally, and some company's retain the efficiencies from EOS as profit until/unless they need to for competitive market reasons.
Or: since the car is actually more expensive out-of-pocket even after the price "drop", they're simply doing this to reduce the sticker price they quote on all of their marketing materials.
https://assets.bwbx.io/images/users/iqjWHBFdfxIU/iqPFhpeWEIS...
Article: https://www.bloomberg.com/graphics/2018-tesla-tracker/