It’s a worse than an honor code violation or crying wolf. It is libel, slander and defamation if untrue, and the facts seem to be all on the fraternity’s side here.
I hope there is a code of conduct that all students are expected to follow, and that honesty is mentioned in that code. Making a false accusation, and one that has caused a lot of misery for innocent people, should be plenty of cause for expulsion, criminal charges, and a huge civil lawsuit.