Maybe look at an actual dictionary for a definition?
All the definitions are basically the same - variations of "right-wing + authoritarian".
I can see that Hearts of Oak are far right-wing, and apparently anti-immigration.
But I can't see any immediate evidence of them satisfying the other conditions of actual authoritarianism.
Whereas the TRAs meet most of the conditions of authoritarianism, and only really escape by self-identifying as "left".
So I think "fascist" fits the TRAs better, as it is a good description of what they DO, even if they would claim different political motivations for their actions.
Hearts of Oak may share some right-wing beliefs and reasoning with conventional fascists, but it doesn't automatically make them fascists. When I see them actually whipping up mobs like the TRAs do, and trying to get people fired for disagreeing with them, I would have to reconsider.