Foul! I cry!
Let's begin with one fact: where the author alludes to the ignition of the paper backing on fiberglass insulation, he fails to mention that all UL-listed insulation has a paper that is very, very resistant in terms of spreading a fire or flame. How resistant? In flame-spread tests, the paper typically has exactly the same behavior as aluminum foil.
IMO, a fire, or heat source, caused by a staple damaging the wire would be a point source, and any fire / charring / damage would spread from that point is all directions - not solely along the path of the wire. Like a weldor at work, the heat is at the arc, and not in the cable.
I have seen a few examples charring like that in his pictures, and in every case the cause was massively overloaded wires, over an extended period of time. That is, the 30-amp fuses on the 15-amp wire. Such overlaoding is not relevent to arc-fault technology.
Even if a sustained arc took place in a BX assembly (no matter if it is really AC, MC, FMC, or LTFMC), I would think the arc would ground out through the metal jacket, and that the metal would serve to contain the heat within the cable, making complete circuit failure more likely.
Following up his emotional appeal by casting aspertions on critics is dispicable. Considering the resume listed at the end of the article, we can only assume that he speaks for his employer, Eaton, which manufacturers AFCI breakers.
I am more concerned by his description of a 'save' by AFCI's. "These events (presumably the event that I assume led to the AFCI tripping) saw the studs being warmed and there wasn't enough time for charring to begin to take shape." Wait a minute ... I thought the article started with 'the electrician' following the path of charring? I'm confused. Yes, we're talking the same person, the same event as at the start of the article.
As with the 'global warming' crowd, it appears that AFCI advocates are singing the same song: "Trust us, we know what's best for you. There's research, but we won't let you see the data. Anyone who opposes us is a bad guy."
I say: If the technology is that important, and he cares so much about our safety .... I expect him, and his employer, to enthusiastically endorse the use of AFCI devices, rather than opposing them. Let's make it both easy, and affordable, to extend this protection to the very homes most likely to have that penny in the fuse box.
