As a UI grad here are some other things to chew on. This lawsuit only applies to graduate housing, not the dorms or other UI owned on-campus apartments. Yes, there are 21 year olds who live in the dorms etc.
There is no state law that says one cannot have firearms on campus at UI, ISU or BJC, excuse me, BSU. The last time a law came up to cover this under the state pre-emption law, the regulation of firearms was delegated to the schools because none of the politicians in the state wanted to possibly get their hands messy on this one. Each of the 3 major state schools have "rules" that state you cannot carry or have guns on campus and they are enforced by threat of expulsion. Keep in mind those rules only apply to the students. The rules are for both on-campus housing and the campus grounds in general. This post covers UI primarily, but ISU, BSU and the assorted community colleges all have virtually identical rules for firearms and their possession.
As an alumni and literally from the day I graduated I could/can carry on campus and I do every time I go back and visit. That said there were some events I was personally involved in that prompted me to carry on campus anyway. Concealed means concealed at that point.
Here is the statute deferring regulatory power to the school. You'll notice the UI is mentioned specifically, that is because the school was founded before the State existed and is considered a political subdivision of the State of Idaho. Look for subsection 5, part C
The University rules on firearms in University housing
General University Rules, Focus on Section H
Subsection C is interesting, they have no legal means of enforcement and as noted in H4, it only applies to students and employees/faculty. The range in Memorial Gym is run by Army ROTC, the general student body no longer has access to it.
Student Code of Conduct, Art VI, Sections 9-12
To sum it all up, if you are a student and are on University property, you have no 2nd Amendment rights unless you are wiling to risk expulsion. It is not illegal, just in violation of the University's rules. They can call Moscow PD, but in the end MPD has no grounds to detain unless you are in violation of city or state law. At most the UI could have a non-student trespassed, which would be hard to do since it is all Idaho owned property. Luckily the Greek System isn't covered under the housing rules. When I lived in-house we had enough guns to arm a small army, and yet with all of the partying we did, no one got shot...