Left the coals glowing with the wind kicking up and they re-ignited, probably.
Starting a bonfire with wooden pallets may not be a good idea unless you are out in the desert at Burning Man. Doing that near a pine forest may not be a good idea.
We had a burn pile from a “controlled” burn that smoldered over winter and reignited in the spring, joined up with another Forest Service ignited fire and eventually burned 350,000 acres.