Every backyard chef knows you have to wait until the coals achieve a coating of ash.
Yep. Looks like Lurch’s believers didn’t wait long enough and the coals flared:
“There’s a reason the bag tells you to wait until the coals are covered in gray ash. A fire that might seem moderately hot while the coals still have some black will very rapidly rise to inferno levels as the coals continue to ignite.”