It's a cash payment to Tesla for a feature that doesn't yet exist, so technically they owe you something until they deliver FSD. If you bought this, you would have been owed $10k but in the form of a self-driving feature. So until they deliver that they technically owe you money, but they owe it to you in the form of FSD.

It’s a “loan” insofar the interest is paid out in over-the-air FSD updates and the principle is irrecoverable.