If you had read about this story, you would know it was 18 minutes from the plane first touching the ground to being evacuated. This includes the time it spent careening down the runway with a massive fireball.
The discrepancy between "can be evacuated in 90s in a simulated emergency" and "actually evacuated in 18min in real emergency with untrained members of the general public (with 100% survival despite the inferno)" just doesn't strike me as that problematic.
The important measurement is time from plane stopping to passengers getting off.
I have nothing but applause for the JAL crew, what they pulled off rivals the Miracle of the Hudson.