Great point by Jonathan:
Sorry Jonathan. Not all of us can be as smart as you.
All jokes aside, again, I think the problem here is defining terrorist strictly as the work of "foreign attackers" is really dubious. Newsweek certainly had no problem identifying Bill Ayers as a "former terrorist" in its subhed back in 08. I'm not in their newsroom. But I'd be very interested to see whether they debated this.
The charitable interpretation is that the Weathermen were an organized group. But it's not one I buying.