That video is incredible. It's hard to estimate size from the shaky footage late in the video, but I would say the fire grows to be almost 50 meters wide in the course of... three minutes? And that's with a dozen men trying to fight it. I was looking at some other grass fire videos and found a great demonstration by a fire department [1]. It's pretty clear that even on a calm day in short grass your window to stamp out an accidental fire is perhaps 10 seconds.

1: https://www.youtube.com/watch?v=rcYVt0DMlos