Electric grid as a cause? No, not really. Every tower is fed from whatever local distribution circuit is available. Many different utility companies, with their own operating and control systems. Now, there might be some centralized cellular operations centers located here and there, but it would take quite an effort to shut several down at the electric utility level without causing other outages. Plus, I’m certain that the larger facilities have backup generators.
Might have to do more digging, but I don’t see a coordinated attack on the power grid bringing this about.
I agree. More likely an attack on the cell network; perhaps like ECM jamming, interference to that range of frequencies.