Here's how I see new cars being sold as inventory cars.
The stores get the notice to move as much product as possible. Discounts on inventory cars OK'd. Inventory cars include demo cars (sit in the showroom), test drive cars, and service loaners. So they sell all those cars, and order their replacements -- stores have to have demo, test drive and loaner cars, and have to order replacements as they sell them.
Normally, inventory cars have a minimum amount of time or mileage they have to reach before they are eligible for sale. To accelerate sales, this waiting period was waived, and they could be sold immediately upon receipt, or in some cases it looks like, while they were still in transit.
This is probably what is upsetting to Elon. The waiting/mileage period that inventory cars needed to accumulate before sale was a reasonable reason for a discount -- the cars racked up miles and wear and tear during that period. Selling the car when it was still brand new, before it had served its purpose as an inventory car, is just like selling new cars at a discount.