Yes, and both the FBI and the (numerous) news outlets covering the story handed the public a handbook on how it was done.
Shooting transformers with a high powered (hunting) rifle creates 2 holes in the unit, allowing the mineral oil contained within to bleed out, and the internal components - no longer propely cooled - blow.
I'm not telling you anything 10 seconds of Googling the California substation sabotage articles won't.
Deer season in parts of North Carolina runs from Nov. 21 through Dec. 10th, making rifle fire out in the countryside something area residents have become completely deaf to and unconcerned with, compounding the "earwitness" problem. People most likely don't remember hearing any firing, and they'vre oblivious to it in that part of the country, this time of year.