If a manager mentions a health issue that an employee had before (cancer) to another employee or accuses the employee who had the illness that the former illness is effecting her judgement at work, is that a HIPAA violation?

If not, is it a law violation. If yes, which one and is there a remedy that the person can seek?

Does this person work in a medical setting?

If what was said is untrue it sounds more like slander than HIPAA.

No, the person doesn't work in a medical setting. The employee did have cancer and is now cured, so the statement was not untrue.

HIPAA is the Health Insurance Portability and Accountability Act.

So medical records were not being discussed only a patient's condition. Please correct me if I am wrong there.

I don't see that HIPAA laws were violated since there was no specific disclosure of medical records by a medical professional in a medical setting.

While it may be possible, you are walking a very fine line there and chances are HIPAA was not violated.