... flipped the tug and got crushed by it.
There's a lot of ballast in those tow tractors. It would take a significant event to flip one.
If it was an aircraft tug. The article is poorly written but I suspect it was a baggage cart tug, not an aircraft tug, because ramp workers flip baggage cart tugs surprisingly frequently.
Aircraft tug drivers, when they crash (and they do), usually crash into the aircraft itself, not the bridge or other vehicles.
Drive under the overhanging aircraft ramp. Decapitated or crushed perhaps?
Tragic slow-speed accident.