Gluten isn't a particular molecule. It refers to the mix of proteins found in the wheat tribe of the family Poaceae. Rice has certain proteins and prolamins, but they are not those found in wheat. When people refer to gluten in the chemical sense, most people mean gliadin and glutenin. Rice has neither.

In what way do you mean rice has gluten? Glutinous rice is 'glutinous' in the Latin sense of the word -- it's sticky (like many plant products). It does not mean it has gliadin or glutenin.