Typically ultrasonic sensors are designed to only return the distance to the first object. They send a pulse out, then time until that pulse comes back from a reflection, and that is the result. They ignore any remaining returns from other reflections.
It may be possible to modify or design your own ultrasonic sensor that pays attention to the other reflections as well, giving multiple outputs from multiple objects, but unless you control the environment carefully it can be very complicated to do well.
But the answer to your question is no, unmodified ultrasonic sensors do not perform multiple object detection.