The US PATRIOT Act defines domestic terrorism as: A person engages in domestic terrorism if they do an act "dangerous to human life" that is a violation of the criminal laws of a state or the United States, if the act appears to be intended to:(i) intimidate or coerce a civilian population; (ii) influence the policy of a government by intimidation or coercion; or (iii) to affect the conduct of a government by mass destruction, assassination or kidnapping.Additionally, the acts have to occur primarily within the territorial jurisdiction of the United States and if they do not, may be regarded as international terrorism.
The Department of Defense defines it as such: The calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.
So, unless these guys have some religious or political reasons for doing their robbery, or wanted to coerce the local population in general, they will argue it's not terrorism. However, that they knocked out the power in order to cause a larger law-enforcement problem to cover for their robbery this MAY fall under the idea of "violence to inculcate fear". While the charge may not actually hold in court, the AG can put the charge up anyway.