2.) Anyone can be a terrorist. Even a President. If he truly attempted to incite a Coup D'Etat, I don't feel any reason not to call him a terrorist and the people who followed a terrorist... a terrorist.
And they thought they were following the word of the President? That has been thrown out since
Nuremberg.
So, yes. I agree with you. They clearly thought they were following the President's Instructions. The President's clearly illegal and ill-thought out instructions. The President's clearly vile instructions that if Obama and/or Biden (or God forbid Hliiary) issued to Antifa, these Proud Boys et al. would be frothing to get on the firing squad to execute those followers of the Presidents' orders that they would deem terrorists.