The same applies to fire in the home - if you can't put it out right now with whatever comes to hand, you've probably lost your window of opportunity to fight the fire. If your sofa or curtains catch fire, there simply isn't time to fill a bucket or fetch a hose. If you don't have an extinguisher to hand and can't snuff out the flames with a blanket, you need to run.
You often do stand a chance if you keep your wits, assess the situation, and act sensibly without any delay. I know everything is easy from my armchair, but can't help noticing how in the grassfire video nobody seems to be doing anything worthwhile while the thing is still manageable. In that kind of dry grass, jackets should have come off and smothered the fire within the first seconds, no panic and no danger.
Best bet, if possible, would be to improvise a barrier xx meters away so when the fire reaches there it stops by itself. Easier said than done.
https://www.avensafetytools.com/product-category/non-sparkin...
I have no idea whether this story is the whole truth, but it's perfectly plausible - in extremely dry conditions, a tiny ember can become an uncontrollable fire in a matter of seconds. The speed of a grass fire can be truly frightening. Take a look at this video:
https://youtu.be/F79tkSKstxY?t=10
The fire in that video was started by the heat of an exhaust pipe, but it could have just as easily been caused by a spark or a cigarette butt. If a fire like this started in front of you, how sure are you that you'd be able to extinguish it single-handedly? What if it started behind you and it got a head start of a few seconds before you noticed it? If you were dressed in shorts and sandals rather than fire-resistant boots and overalls, would you even stand a chance?
A moment of hesitation or distraction is all it takes to lose control of a grass fire. Based on the account given, I can fully imagine the desperate and ultimately futile effort made to extinguish a fire that rapidly spread out of control.