Looking at the picture, my theory may be wrong. There is a black spot on the torch too far from the hot glass.

My other theory is that the flames where so bright they had to edit the footage. Old film developers had a technique to darken an area called “burning”. It was not so precise to cover over the flame so the are around the bright spots got darkened as well.

Modern HDR can have a similar effect. When an algorithm can’t be sure of how dark an area between a dark and a bright spot must be, it make the transition gradually causing the “HDR Effect” where, for example, the sky gets brighter the closer you get to the horizon, building, subject.