I think their distinction is that they’re selling the hardware, which is capable of controlling the car just fine. So the thing you’re paying for is delivering as promised. The software is a separate project, and you could theoretically load whatever software on the hardware you wanted. So the fact that the software is glitchy is not (in the view of the company) something you can hold them responsible for. You paid for hardware, you got hardware. What you do with it is up to you.

This is at least what I remember from a years old Wired article when the comma one was being developed.

Whether that will actually hold up in court is TBD, considering how closely coupled the software is to the company and hardware.