1. From 2016-2019, Tesla said that FSD would someday be available via a $10k software update, and that all their cars came with all the hardware that would be required to use that update.
2. In mid-2019, Tesla started installing more powerful hardware on their new cars.
3. They have now started offering FSD as a subscription service. They do not offer the one-time $10k FSD product.
4. The FSD they are offering via that subscription service requires the new hardware. Tesla owners with the old hardware who want to use the subscription service will have to pay $1500 to upgrade the old hardware.
It comes down to whether or not the subscription FSD counts as the FSD from #1, or if it counts as a different FSD product with different requirements.
Legally, I'm sure they are in the clear because the subscription product is in no way even remotely FSD and so they can claim that #1 is referring to some future real FSD.