The most likely cause of getting heatburn from eating glutinous rice may be the relatively rapid fermentation process of the heavy amounts of starch and the additional acidity produced by the fermentative chemical process between the starch and the acidity in the stomach.
A Mexican lady went on a tour of Japan. After eating her first Japanese meal, she had severe heartburn that night in her hotel room. She said that she is Mexican, and Mexicans eat a lot of rice and corn and flour tortillas and she never had heartburn. She described Japanese rice, i.e., glutinous rice, as too “acidic and this acidity from the Japanese rice brought on my heartburn in my hotel room.”
The starch and acidity reaction happens with glutinous rice but not with long grain rice which has very little starch in it. The famous rice porridge of southern China as well as homemade glue that Chinese kids used to use as paper paste are made from glutinous rice. Long grain rice does not make porridge nor paper paste because the rice does not get very soft, and long grain rice does not retain as much liquid as short grain glutinous rice does.