They are delivering a superior battery with more capacity and performance than what you actually ordered. The only difference is that they figure to make up the difference when eventually the car is sold back to tesla and then they can "activate" the extra part of the battery of the owner didn't already pay for the extra upgrade somewhere along the way and then resell the car for much more than what they paid since the car is now a couple models better.
But maybe I didn't want to the bigger battery in my car? Maybe I would have preferred a lighter car? Or I have some other reason I wanted specifically the small battery? Do I have the option to not have the optional-upgrade-enabled battery? Do I have the option to give the car back because it's not what I ordered?