Of course not. They aren't exercising violence - they are merely occupying a property. They didn't pick a target which would incite fear in the masses - on the contrary, they went for a secluded wildlife refuge. If they are terrorists, then so is Occupy Wall Street or Black Lives Matter's more peaceful protesters1. They are also not trying to achieve a political goal. They do not want a law introduced or repealed, they are standing their ground against a decision they perceive to be unjust.
Are they reasonable? No. Are they terrorists? Also no.
1 - I am, of course, ignoring the less peaceful "protests" in which they decided that burning down half of their own town is a good idea.