Tesla FSD (but not autopilot) deliberately tracks the car in front of it, as well as the lane and tries to follow that car (and takes it as a safety signal and slows when the car above swerves out of the lane). It's interesting behavior, and usually annoying, but this is why it's there.
Most radar cruise control is set low on the bumper which allows visibility into the vehicle in front. My 12 year old car with adaptive cruise control will sometimes begin slowing when the car two cars ahead starts slowing. Sometimes because it requires a truck or suv or otherwise a vehicle with a higher ride height for radar to pass under. When it’s a Miata in front of me, I will only track that Miata because it’s so low. At the same time.. I can see over these lower cars. The ford flex however is a car that stands out as a low sitting vehicle that is rather tall for its ride height.
That said none of this matters if the object or vehicle in front of the following car is stopped. The radar system will ignore it as part of the background.
