I speak not as an ASUCD Justice, but as a private tudent who is extremely well-versed in both parliamentry procedure and the ASUCD bylaws. Commission Chairs have a extremely wide degree of latitude as to how to run their meeting. Until and unless a majority of the body votes to overturn his ruling, the chair is pretty much free to do as he pleases. That is not always the most politically sound strategy to run a committee, but technically well within their right to do so.
So despite your ardent desire for Rivera to be wrong, he wasn't.