It's not entirely true: if someone pays me to sell my house/car/jet, and promises to give it back next month, we can work something out if the money is good.
I'm pretty sure most new car sellers don't even own the cars they're selling: they can only afford to pay the manufacturer after they've sold the car. The entire fiat economy runs on debt.
I noticed some replies pointing to that comparison. I'm not sure short selling and consignment operations (or whatever you would call it) are an appropriate comparison. Short selling is speculation, whereas Tesla has an ongoing business operation with real cash flows.
I disagree with him fundamentally though. Stock owners should be able to do whatever they want with their shares, including lending them to short sellers.