It doesn't matter what the ignition temperature is. The goal is to keep items from continuing to burn on their own, that they are 'flame retardant':
Pyro is a very intermittent heat and flame
effect, compared to tests that materials are subjected to, which, depending on use, are either 45 seconds sustained flame, 10 minutes, and 30 minutes. FYI, the flame temperature of most of these tests are in the +/-3500F range. Some tests require a closed oven to increase the surrounding air to 1000F, with ample new air brought in to sustain the fire. There are thermo sensors within the testing
unit to verify temperature. Seems somewhat higher than the outdoor, flowing air of this event, and the non-sustained temperature exposure of the
pyro.
With that in mind, lab tests are not real world situations. In this situation, it seems that a lab test would maybe have been more rigorous.
Also, US codes for flame resistance aren't proscriptive any more, meaning they don't say 'items need to be flame retardant treated'. They say 'items need to meet these particular fire tests and specifications', and how you get there is not dictated by code.
The biggest issue in my experience with flame retardant treatments is that people use them improperly for things that the FR chemicals are not designed and tested for. Like today, people wanted to apply a flame retardant designed for polyester fabrics onto urethane foam that's applied to a wall. They not only have a mismatch in the FR chemical design vs. application, they also have the a mismatch in what testing and item usage the chemical had been tested to meet.