Here is a theory: If you turned the cruise control stalk upwards instead of hitting the blinker upwards to turn right (or if your foot pushed it etc.), it would have engaged cruise on current speed. A constant speed! If you did this while your foot was away from the gas pedal and the car was decelerating, it could still have resulted in a steady and higher than normal speed (whatever speed your car had when the stalk would have been moved) coming out of the turn... while your expectation was the car slowing down because gas pedal is not pressed. A witness saying the speed was constant would indeed suggest that at some point entering the corner, cruise control was enabled at the current speed, thus maintaining a constant speed through the corner, while your brain was expecting the car to slow down since no pedal was being pressed... I've said it before, the confusing Tesla cruise control setup is, well, confusing. Setting cruise the same way you flick a stalk (either up or down and even pulling does different things depending on situation) for blinkers could be the reason why there are reports of this issue happening especially when turning a corner... You said your style is to not brake or accelerate into corner, so it sounds like you were not pressing any pedals. If cruise got enabled at any speed in that scenario, you would not have been prepared for it, since your expectation was that the car would automatically slow down coming out of the corner. Lacking data, this is speculation of course, but I could see this scenario happening. There have been others on TMC reporting similar incidents. For example Audi requires you to press a button at the end of the stalk to set the cruise speed, which is IMO a lot better setup and much less confusing.