From the UN Security Council:
"criminal acts, including against civilians, committed with the intent to cause death or serious bodily injury, or taking of hostages, with the purpose to provoke a state of terror in the general public or in a group of persons or particular persons, intimidate a population or compel a government or an international organization to do or to abstain from doing any act, which constitute offences within the scope of and as defined in the international conventions and protocols relating to terrorism, are under no circumstances justifiable by considerations of a political, philosophical, ideological, racial, ethnic, religious or other similar nature,"
We're splitting hairs here. The hillbillies in Oregon deserve to be arrested and prosecuted for whatever laws (quite a few, I'm sure) they have broken. Honestly, calling them terrorists gives them too much credit. They want that attention.