Some important background.
https://marylandmocktrial.wordpress.com/get-involved/
These Mock Trial courses are not something students can just register for on their own. According to UMd website, they all require permission of the instructor, and that each student who wants to register email Graber and explain why they want to take the course. 
That's makes it likely that these were NOT all students in the course, but students on an email list of those who had inquired about getting permission and/or already had permission. 
There are currently 3 such courses at UMd, and according to the articles others have cited, Graber was slated to teach the 388 course, which is the most advanced 388 level and can be repeated up to 3 times.
There is a 217 Intro course called "Mock Trial 1", and a 319 intermediate course.
IOW, it is likely that nearly every single student in Grabers course had taken at least 1 and up to 5 prior mock trial courses. 
His daughter said that "none have prior Mock Trial experience". That would be rather easy to verify, and if true would make it beyond reasonable for them not to admitted and told to take a different entry level course. 
BTW, Graber is apparently among the best Mock Trial coaches in the country, according his record of victories in national competition. 
Finally, it is too bad for the sake of comedy that Graber wasn't fired for sexual harassment.