Terrorism is just a label,
Terrorism isn't just a label, it's a big part of the budget process.
When I was a small boy (think an evil The Beaver) I used to go by the city water tank on the way to the pool. I'd throw small pebbles at the tank because it made neat noises when I could hit it, and different parts "ping"d differently.
It's not hard to imagine that were I somewhat older and a lot of dumber I'd wonder what other things in remote areas sounded like when hit.
And I always used to listen for spoil-sport Adults and run at any noise, just like these guys (cars are not hard to hear at night).
The main reason I have trouble seeing this as a precursor attack is that they took such a big risk of getting caught. But the grid really is fragile: nobody likes redundant transmission lines in their back yard, nor the cost added to their electric bills.
PS. Hollywood always portrays the adversary as an Evil Genius, but sometimes they're really an Evil Moron.