This 'factoid' example of internet 'science' illustrates many things - none of which are discussed in the text.
The first is that this video dovetails nicely with a recent article in IAEI News discussing the imagined OPCI, or "Out of Parameter Circuit Interrupter. Beam me up, Scotty. I just can't wait for the next wave of hysteria-driven code mandates.
"The cause of most electrical fires." Really? Whay happened to overloaded extension cords or the mythical errant Romex staple? What of the penny fuse, aluminum wiring, or FPE breakers? Nope - it's been our wire nuts all along.
Bursting into flame at 55C? UL standards already require such plastics to be self-extinguishing, and I've yet to see a wire nut rated at less than 105C. That, btw., is higher than the rating of the wire insulation.
A fire needs air - and a closed box in a wall stuffed with insulation isn't likely to let much air in. You know those wastebaskets at the mall? Those are designed to restrict air entry- which is why you have probably seen one smoking, but not with flames shooting out. Same principle would work here.
I've opened up plenty of boxes, and found all manner of poor connections, but finding a heat-damaged wire nut has been quite a rare event.
"Joule effect?" What is a joule? Nothing but a unit of energy measurement. Get anything hot enough and bad things will happen.
GFCI didn't work? No surprise there .... they were never seen as a fire protection device. Breaker didn't trip? Well, breaker size aside, you can do some serious welding with the power used by the common hair dryer.