It must be so frustrating for both parties. One person has to drag themselves to the Dr. When they are already feeling too sick to go to work. And the Dr. has to go through the motions for a minor issue that does not require intervention. Just so an employer is satisfied that the employee isn’t lying and god forbid enjoying their day.
This is the best answer. Not that you even owe them this much of an explanation. But it provides enough detail to satisfy them and succinctly tells them in corporate language to fuck right off.