Watch the sun. It is monitored all the time, and the information is public. Even a casual familiarity with solar events and how they effect the earth can show you pretty conclusively whether someone is lying about that.

There was a brief X-class flare on the sun, along with an M-class flare, but no coronal mass ejections. There was enough energy to ionize the upper atmosphere in places, but it was only mildly disruptive to radio transmissions. It was certainly not an event that would cause the kind of widespread cell phone disruption people have reported.

My guess is that they are using an actual sunspot event as a cover for having to shut off service, most likely to accomplish something they can't do with a fully-buzzing grid. Whoever they happen to be in this case are counting on the fact that most people will just believe what they are told, and that if any start to look into it, they will find evidence of a real event that seems to confirm the official story. It doesn’t, but most people won't know that.

https://www.youtube.com/watch?v=QPdcXkylbfk