Acid reflux, according to Wikipedia, is caused by:
... poor closure of the lower esophageal sphincter ...
This in turn causes stomach acid to rise into the esophagus, which is regardless of the levels of acid present in the stomach.
The WP reference given is NIDKK, who say that a weak sphincter is caused by:
- increased pressure on your abdomen from being overweight, obese, or pregnant
certain medicines, including
those that doctors use to treat asthma —a long-lasting disease in your lungs that makes you extra sensitive to things that you’re allergic to
- calcium channel blockers—medicines that treat high blood pressure
- antihistamines—medicines that treat allergy symptoms
- sedatives—medicines that help put you to sleep
- antidepressants —medicines that treat depression
- smoking, or inhaling secondhand smoke
and make no mention of the stomach contents as a cause.