I am guessing that her hair may be bleached and/or colour treated which is why it really could not take the heat. A second lesson is that you should really know how hot the curling irons or flat irons are. A final tip is that when using heat, your hair should not get so hot that you cannot touch it.
I know some people out there are laughing at this poor girl but I was really sad for her, she looked beyond shocked and could not comprehend what was happening. Lucky for her that it was just the first section and she can hide that part while it grows back. I am glad that she posted the video, honestly people need to learn to respect heat tools and there is nothing like this video to understand responsible use. Normally heat damage will happen exactly like this but will take several weeks or months, seeing it in one flash is really sobering.