The fascists in the coup wrongly believed they were insurrectionists taking back their government. That's what makes this so hard to establish the difference between the two.
For example, let's imagine that day turned out the way Trump had hoped and the angry mob outside pressured Congress into overturning the election. That would have been a successful coup, and the ignorant fascists would have would have celebrated the restoration of democracy due to their insurrection.
If democracy would have crumbled under the weight of the coup, at least 80 million Americans would then have participated in a grassroots insurrection to take back our government from the fascists -- and that insurrection would have been fully justified by the facts. Everyone who participated in that insurrection would have genuinely been a hero.
Here's the key point: Trump has so completely deluded his followers that they believed they were participating in a righteous insurrection when they were actually aiding and abetting a coup. I don't offer that as a justification for what they did, and they should face severe consequences for their foolishness to serve as a deterrence for future coup attempts, but in our age of fake news and facts created through repetition of lies, their stupidity and criminal behavior is easily understood.
The real problem here is that we are willing to forgive Trump and politicians like him for incendiary rhetoric because we give Americans undue credit for being intelligent enough to parse truth from fiction and act accordingly. When ignorant thugs believe political rhetoric and act criminally, we pity them, and occasionally we prosecute them, but we always give the politicians a free pass. American politicians know they can incite violence with falsehoods with no consequences whatsoever. That's the dangerous precedent this tragedy has entrenched into our political discourse.