The way I heard it was the vehicle went around the gate (didn't hit it) and missed the cell tower and veered toward the drop off.
That leads me to believe it was going straight and one side dropped off causing it to roll.
I have rolled over in an SUV where the bags did not deploy and it is as you described. My friend was driving and went around a country road curve too fast.
She then over corrected (twice) and we ended up going the right way, following the road, but were partly in the ditch. The ditch was steep enough where we felt the SUV slowly leaning towards the side until it eventually flipped all the way over and we ended up upsides down. Totaled her Jeep Grand Cherokee ($12k in damage), but the air bags did not deploy. Probably the scariest thing I have been through, and we only rolled once!