While the situation you are describing MAY have occurred - billing departments make mistakes.

The individual here may have had their bill mailed to the wrong address, may not have known to expect a bill because they incorrectly expected a service to be covered by insurance or the medical office could have miscoded something and the individual is now incorrectly receiving a bill for a service that was covered by their insurance.

No need for your lecture - our medical system is overly complicated, driven by profits and almost as morally corrupt as the insurance industry.