All that snow is going to do next to a jet fuel fire is create a lot of steam.

The crash kicked up a lot of snow into the air, making me wonder if that helped suppress the fireball, as it seemed to die down very quickly. On thing leading to me think this might have happened is video from the recent firefighting in California, where the spray from the firefighting aircraft seemed to snuff out the flames as soon as it descended into them, before it reached the ground.

A fire can be extinguished with diesel (jet fuel is pretty much just cleaner diesel / kerosene) in cold conditions, I know because I’ve done it.

It takes a fair amount of heat / pressure to ignite jet fuel, easier if it’s vaporised.

Why were you trying to extinguish a fire using diesel?

I would guess they were not trying to extinguish a fire with diesel and accidentally learned you could.

Indeed. It was about 0 degree Celsius, camping and we were trying to get a bit of a fire going for heat. I won't do that with petrol as I value my eyebrows, ended up having to thin the diesel a bit with petrol as we discovered splashing diesel on a small flame on damp wood doesn't help at all.

...and absorbing lots of heat as it evaporates.

There's a reason water is used for firefighting.

Also the wing broke off early so the plane continued away from the initial fireball.

And the fuel spilled both away from the fuselage and onto snow, which both kept the main focus of the fire away from people and limited development of the fireball as well.

Kerosene (Jet-A) is relatively nonvolatile and tends to burn most violently when dispersed in air. It's not quite as heavy as diesel fuel, in which you can extinguish a lit match, but conditions in this incident probably limited flame development considerably.