I cannot really answer your second question. Not only were their conclusions different from mine, but they were different from those of the vast majority of experts in second-language learning. The problems with the data mainly involved statistics being improperly interpreted. For example, they calculated the dropout rates from immersion programs from one year to the next, but their calculations were wrong.
Moreover, they completely ignored some of the research in preparing their report. I have written much more detailed documents on this subject. I can send them to you if you are interested.