The thing to remember is that the college admins are not necessarily going to be interested in reasonableness or justice (perhaps they are, but assume nothing). Operate on the assumption that they want to get you, and keep in mind what happened with the
EMT student in Ohio, who got railroaded over being a self-defense advocate.
The "empty holster" thing was a First Amendment statement, but could be taken as an attempt to intimidate ("I own a gun. I didn't bring it TODAY.").
Explain the symbolism as part of an advocacy for concealed carry rights, so they understand what he was trying to communicate.