The statement from the dissenting opinion of tinker v. des moines court decision that best supports the reasoning that the conduct of the student protesters was not within the protection of the free speech clause of the first amendment is :
In cox v. Louisiana, the court clearly stated that the rights of free speech and assembly "do not mean that everyone with opinion or beliefs to express may address a group at any public place at any time
A good logical prediction is something big might happen, maybe a volcano eruption, or maybe something is chasing them (besides). Lost is terrible, they could get eaten.. They might be getting hunted by a hungry tiger.