And if they have no information other than these numbskulls having igniters and fusers in the car, and being near a critical military facility? What then? Is it against the law to possess igniters and fusers? Is it against the law to drive on that road?
If that's all they've got, you want the FBI to publicly state that they're terrorists?
A case built on those two facts wouldn't even make it to court.
I'm not saying these guys are pure as the driven snow -- creating fear could be their idea of fun, like that group of Florida ME med students five years back, or it could be a case of intentional in-your-face provocation, like the flying Imams -- but if what the media is reporting are all the facts there are, for the FBI to call this terrorism, as it is defined in our laws, without any further facts, would, as you say, put their credibility in the crapper.