For what it's worth, I've tried and failed to reproduce this on my Model 3. I've driven next to trucks, motorcycles, under overpasses, under very-low overpasses, near pedestrians, and even passed camels and horses on the side of the road. No phantom braking.

That said, when using the lane-assist, I do prefer to keep my foot on the accelerator pedal anyway. To increase range, I try not to get into regen at all unless I actually do want to brake. I feel that the cruise control is to strict in keeping a particular speed in hilly areas, and I live and work in hilly areas. Let the vehicle speed up in the dips and slow down on the peaks, just like all the other cars (probably manually driven) are doing.