It seems from the Gemara that the argument whether rice and millet can become chametz are physical arguments and not halachic ones. Certainly no one quotes a tradition as to one species can become chametz. How does one explain this disagreement?
In general, an argument which seems to be based in the reality of the
physical world is explained as follows:
Certainly, rice ferments to some extent. However, it does not ferment to the same extent as wheat and barley. The argument here is whether this degree of fermentattion qualifies to consider it real Chametz or not.