How could the sysadmin not have seen this: http://lct.msu.edu/guidelines-policies/bulkemail.html
" # Permitted uses for broad cross-University mailing. Bulk e-mailing may be used only by University offices to send communications necessary to the normal course of business and which typically require some official action be taken individually by recipients. Such permitted uses include:
* Dissemination of urgent information of health and safety concern for students and University employees. * Communication of information regarding changes of University policies or procedures, or actions that affect employment or compensation status, or status as a student. * Regular communications (for example, to University employees) that are required by law, regulation or University policy for which bulk e-mail may largely replace paper transmittal.
So, according to their own policy, mass emailing of "...information regarding changes of University policies or procedures, or actions that affect employment or compensation status, or status as a student..." falls within acceptable use. That is assuming that this change to the university schedule is a "change in policy" or "affects employment". I don't see how that wouldn't be the case.
Key part you are missing is "University offices" I don't think Student Council is a University office. It comes down to this they want to control the message.