Legal Question in Criminal Law in California

In order for a magistrate (judge) to hold somebody for trial at a preliminary hearing, they have to be satisfied that there is proof of the crime (and that includes every element). It is a very low burden of proof -a "probable cause" standard, so in the case where there is some evidence, often, judges will bind a defendant over and let a jury decide.

Of course, that's not the end of the line. If there truly was not enough evidence, your grandson's attorney should be filing a 995 motion to challenge the sufficiency of the evidence presented at the preliminary hearing.

Without having heard the testimony or reading the transcript of the preliminary hearing, that's the best I can do in answering your question.