Passengers heard a loud boom and saw smoke from the engine and pieces of metal flapping, causing masks to deploy and sparking fears of an attack.
This week's peace accord could bring an end to Latin America's oldest guerrilla war, which has caused more than 220,000 and displaced 5 million.
A deputy grabbed the clothing of Jason Binkiewiz, but if he'd held on he might have gone over the banister as well, the sheriff said.
The killing of Edgar Juvanny Parra Zambada, a seafood merchant, is the latest attack on the group's family members.
The attack in Wilkinsburg, Pa., involved one man shooting at partygoers while another hidden near a fence shot fleeing people with a rifle.