"Terroristic Threats" are one way that free speech is under attack. Another is harassment laws. Law student Anya Bargh was arrested for sending an email saying "Let’s celebrate diversity by having the next dean NOT be Jewish." If that isn't protected speech I don't know what is. http://www.volokh.com/2013/05/03/law-student-arrested-chiefl...
Did you actually read what you linked to? The entirety of the allegations go _way_ beyond that single email.
If the police say "We are arresting person X because of this statement, and they also did some other stuff", then this suggests that the statements are part of the charges. But as I said above, it's hard to know for certain without seeing the actual charges.