Could just be good planning if they knew that was procedure after an explosion.
Aside from that, I seriously doubt that just disruption of AT&T services was the objective here. Considering that this appears to have been a rather serious explosion, I guess the intent was more likely destruction rather than disruption.
With the amount of 5G nut jobs running around these days, I suspect that it is far more likely that somebody just seriously underestimated what it takes to bring down a building like this one.
But I guess that time will tell (more). I'm just speculating of course.
But the 5G conspiracist angle actually makes a ton of sense.