Hack the North official statement on ejecting attendees for Facebook joke [pdf]
hackthenorth.com
hackthenorth.com
It is the Universities obligation to ensure the safety of its members, it has these black-and-white rules to ensure mistakes don't happen through lack of direction, inaction or uncertainty.
In these situations, whether threats are real or just a joke, the faculty doesn't gather a panel and sit down and debate the true nature of the threat, they act immediately to ensure the safety of their community. Knowing their policy is a complete evacuation, and likely realising that the comments were a joke, simply evicting Errington and the other poster was likely a cool-headed reaction in lieu of a proposing or interrupting the event.
Of course, all this is irrelevant because the two weren't thrown out because the University was concerned about a bomb threat. This all happened because some random anonymous person complained to MLH that the postings made them feel "unsafe," and instead of telling that person to go pound sand, MLH and HTN cooperated to enforce exactly the same foolish zero-tolerance policies they were joking about.