Even after a large wildfire is extinguished, there are always chances for flare-ups. Remember the fire triangle? A little oxygen can restart an unnoticed hot spot and resurrect a wildfire. The "Set" portion of "Ready, Set, Go!" means "stay vigilant of your surroundings."
From the Source:
"Crews arrived to find 3 to 4 acres burning near the mauka perimeter, about 1.5 miles from the nearest structure, according to Maui Fire Services Chief Edward Taomoto."
"When darkness fell, officials say the fire was still active, and was creeping slowly upslope. According to department reports, the fire grew to 7 to 10 acres and was moving into denser forested areas overnight."