"Hey you should buy this aftermarket autopilot system along with the car. No it isn't sold by Toyota. It's some small company you haven't heard of. No there's no warranty. Nope no safety data. You have to accept all liability for use. Yeah it might kill you and your kids. But hey, you get to be an alpha tester!"
99% of customers are going to walk out of the dealership after hearing that pitch.
A good sales person would talk about any self-driving feature built in (eg lane following) then mention the car is compatible with third-party self-driving products like Comma.ai.
Just like how they talk about brakes, wheels, exhaust on sports cars - all areas customers may mod after purchase.
What's in it for the sales person or the dealership?
What you said would be the case if they had the baggage of "full self driving" marketing over 10 years.
What would the developers tell their partners or friends in confidence? Are their claims in confidence supported by evidence that they made efforts to validate in proportion to the magnitude of their claims? Does that differ from what they say commercially? If so, then they are communicating deceptively to further their monetary interests.
That is not to say that other manufacturers are not communicating deceptively all the time as well, but complaining about truthful statements because they do not exaggerate to the detriment of the user for the monetary benefit of the manufacturer is silly.