Grading scales can and do change depending on circumstances of how the class goes. If a majority of the students do poorly on a quiz worth 20% of your grade, the professor may choose to bump that down to 10% and give a second quiz worth 10%. Perhaps because some students complained the quiz was a poor reflection of what was actually learned. Professors require flexibility to deal with things that happen as the class progresses. A Syllabus is just a basic outline. Seriously - if a test was scheduled on a day where there was a fire in the building and class was cancelled what is the professor supposed to do if he/she can't venture outside of the syllabus?
Universities do not create syllabi, individual professors do for individual classes. Some universities don't even require a professor to give one to their students. I don't see how a syllabus is even really relevant here at all because (University wide) student honor/conduct codes and the like are what actually applies here.
Courts generally stay out of grading disputes (for good reason!)
"University faculties must have the widest range of discretion in making judgments as to the academic performance of students and their entitlement to promotion or graduation." - Board of Curators of the University of Missouri v. Horowitz (Supreme Court)
Not only that the probability of this going to court is zero - the university provided a replacement professor to assign grades instead of failing the class.
I also read about this in another paper this morning and it said that the university had assigned security to this class previously due to its behavior.