what happened was there was another emergency on the other side of the airport where a different plane was having issues so they were sending the fire truck as a precaution. ironic that they were trying to prevent an accident caused an accident to happen. it's another one of those things where multiple bad things happening at the same time. ATC was even repeatedly pleading Truck-1 to stop.
The ATC must be absolutely devestated right now. I can't even believe what's going through his head, but I hope someone is watching over him.
It's insane how little it took for everything to go so wrong. You'd think there'd be gates or something as a second line of "defense" to avoid errors of judgement. Really speaks to how skilled the ATCs are as they avoid these things on a daily basis.