If medication can control a symptom (e.G. Gerd/lpr reflux) does that mean the symptom isn't caused by stress or anxiety?

Stress not by self. Stress may worsen gerd symptoms, but unlikely to be only cause of your chronic heartburn. In the past stress was thought to be the culprit in a variety of gastrointestinal problems, including ulcers and inflammatory bowel diseases such as crohn's disease. Hiatal hernia, diet, pregnancy, obesity are few known contributors.Sometimes genetic.