This report is really stretching the definition of terrorism. Terrorism is basically mass murder accompanied by blackmail. But the purpose of terrorism is to force a government and its society into submission, and that's the missing ingredient here. The scum who formed al Queda calculated in their own minds that if they could murder 400,000 Americans we would "Submit" to the will of Allah. So basically for AQ it was, "Look at what we just did to you. You thought you were invincible. If you don't "Submit" we will attack again and again until you do!" These jihadis are all of the same mindset.
Now let's look at the right wing extremists. These guys are social outcasts. Losers in life who have had misfortune and failure. To absolve themselves of blame for their failures it's someone elses' fault, like the government. They somehow see the government as infringing upon them and they want to live outside its laws and societal norms. But unlike islamic terrorists these guys are not of the same mindset. They all are angry failures for a different and non-united set of circumstances. They probably couldn't get along with each other well enough to form a cohesively large organization. That's why you hear the term "Lone Wolf" so often. I just don't get worried about a bunch of white guys blowing up a jet because they hate to wait in line at the DMV.