The reason everyone stopped to fight is quite simple; they are clearly now encircled by a large group of armed gangsters, and the current situation of the school bus veering off the highway proves that continuing down the highway it is not a safe option.
As Leonard Ethan and the others disembarked from their vehicle, armed with their weapons, they found the road ahead littered with iron nails embedded in shards of broken glass. This explained why the school bus swerved off the road.
The attackers were targeting the school bus that had just veered off the road. They likely first drew the bus driver's attention by firing shots at him, forcing the driver to recklessly charge ahead and lose control upon hitting the roadblocks laid on the ground.
This scenario demonstrated Fairmont's rich combat experience, as proceeding further might have yielded the same fate of immobilization that had befallen the bus.
